diff --git a/backend/app/services/room_manager.py b/backend/app/services/room_manager.py
index 38e65c1..b4a6ff7 100644
--- a/backend/app/services/room_manager.py
+++ b/backend/app/services/room_manager.py
@@ -1,12 +1,17 @@
 import json
 import random
 import string
+import asyncio
 from typing import Optional
 import redis.asyncio as redis
 from app.config import get_settings
 
 settings = get_settings()
 
+# Lock timeout in seconds
+LOCK_TIMEOUT = 5
+LOCK_RETRY_DELAY = 0.05  # 50ms
+
 
 class RoomManager:
     def __init__(self):
@@ -20,6 +25,31 @@ class RoomManager:
         if self.redis:
             await self.redis.close()
 
+    async def _acquire_lock(self, room_code: str, timeout: float = LOCK_TIMEOUT) -> bool:
+        """Acquire a lock for room operations."""
+        await self.connect()
+        lock_key = f"lock:room:{room_code}"
+        # Try to acquire lock with NX (only if not exists) and EX (expire)
+        acquired = await self.redis.set(lock_key, "1", nx=True, ex=int(timeout))
+        return acquired is not None
+
+    async def _release_lock(self, room_code: str):
+        """Release a room lock."""
+        await self.connect()
+        lock_key = f"lock:room:{room_code}"
+        await self.redis.delete(lock_key)
+
+    async def _with_lock(self, room_code: str, operation, max_retries: int = 20):
+        """Execute an operation with a room lock."""
+        for attempt in range(max_retries):
+            if await self._acquire_lock(room_code):
+                try:
+                    return await operation()
+                finally:
+                    await self._release_lock(room_code)
+            await asyncio.sleep(LOCK_RETRY_DELAY)
+        raise Exception(f"Could not acquire lock for room {room_code}")
+
     def _generate_room_code(self) -> str:
         """Generate a 6-character room code."""
         return ''.join(random.choices(string.ascii_uppercase + string.digits, k=6))
@@ -88,78 +118,160 @@ class RoomManager:
         team: str,
         socket_id: str
     ) -> Optional[dict]:
-        """Add a player to a room."""
-        room = await self.get_room(room_code)
-        if not room:
-            return None
-
-        # Check if team is full
-        if len(room["teams"][team]) >= 4:
-            return None
-
-        # Check if name is taken
-        for t in ["A", "B"]:
-            for p in room["teams"][t]:
-                if p["name"].lower() == player_name.lower():
-                    return None
-
-        # Add player
-        player = {
-            "name": player_name,
-            "team": team,
-            "position": len(room["teams"][team]),
-            "socket_id": socket_id
-        }
-        room["teams"][team].append(player)
-
-        # Save player mapping
-        await self.redis.setex(
-            f"player:{socket_id}",
-            3600 * 3,
-            json.dumps({"name": player_name, "room": room_code, "team": team})
-        )
-
-        await self.update_room(room_code, room)
-        return room
-
-    async def remove_player(self, socket_id: str) -> Optional[dict]:
-        """Remove a player from their room."""
+        """Add a player to a room (with lock to prevent race conditions)."""
         await self.connect()
 
-        # Get player info
+        async def _do_add_player():
+            room = await self.get_room(room_code)
+            if not room:
+                return None
+
+            # Check if team is full
+            if len(room["teams"][team]) >= 4:
+                return None
+
+            # Check if name is taken
+            for t in ["A", "B"]:
+                for p in room["teams"][t]:
+                    if p["name"].lower() == player_name.lower():
+                        return None
+
+            # Add player
+            player = {
+                "name": player_name,
+                "team": team,
+                "position": len(room["teams"][team]),
+                "socket_id": socket_id
+            }
+            room["teams"][team].append(player)
+
+            # Save player mapping
+            await self.redis.setex(
+                f"player:{socket_id}",
+                3600 * 3,
+                json.dumps({"name": player_name, "room": room_code, "team": team})
+            )
+
+            await self.update_room(room_code, room)
+            return room
+
+        try:
+            return await self._with_lock(room_code, _do_add_player)
+        except Exception as e:
+            print(f"Error adding player: {e}")
+            return None
+
+    async def remove_player(self, socket_id: str) -> Optional[dict]:
+        """Remove a player from their room (with lock)."""
+        await self.connect()
+
+        # Get player info first (outside lock)
         player_data = await self.redis.get(f"player:{socket_id}")
         if not player_data:
             return None
 
         player_info = json.loads(player_data)
         room_code = player_info["room"]
-        team = player_info["team"]
 
-        # Get room
-        room = await self.get_room(room_code)
-        if not room:
+        async def _do_remove_player():
+            # Get room
+            room = await self.get_room(room_code)
+            if not room:
+                return None
+
+            # Remove player from both teams (in case of inconsistency)
+            for t in ["A", "B"]:
+                room["teams"][t] = [
+                    p for p in room["teams"][t] if p["socket_id"] != socket_id
+                ]
+                # Update positions
+                for i, p in enumerate(room["teams"][t]):
+                    p["position"] = i
+
+            # Delete player mapping
+            await self.redis.delete(f"player:{socket_id}")
+
+            # If room is empty, delete it
+            if not room["teams"]["A"] and not room["teams"]["B"]:
+                await self.redis.delete(f"room:{room_code}")
+                return None
+
+            await self.update_room(room_code, room)
+            return room
+
+        try:
+            return await self._with_lock(room_code, _do_remove_player)
+        except Exception as e:
+            print(f"Error removing player: {e}")
             return None
 
-        # Remove player from team
-        room["teams"][team] = [
-            p for p in room["teams"][team] if p["socket_id"] != socket_id
-        ]
+    async def change_player_team(
+        self,
+        room_code: str,
+        player_name: str,
+        socket_id: str,
+        new_team: str
+    ) -> Optional[dict]:
+        """Change a player's team (with lock)."""
+        await self.connect()
 
-        # Update positions
-        for i, p in enumerate(room["teams"][team]):
-            p["position"] = i
+        async def _do_change_team():
+            room = await self.get_room(room_code)
+            if not room:
+                return None
 
-        # Delete player mapping
-        await self.redis.delete(f"player:{socket_id}")
+            # Find current team
+            current_team = None
+            for t in ["A", "B"]:
+                for p in room["teams"][t]:
+                    if p["name"] == player_name:
+                        current_team = t
+                        break
+                if current_team:
+                    break
 
-        # If room is empty, delete it
-        if not room["teams"]["A"] and not room["teams"]["B"]:
-            await self.redis.delete(f"room:{room_code}")
+            # If already on target team, just return room
+            if current_team == new_team:
+                return room
+
+            # Check if target team is full
+            if len(room["teams"][new_team]) >= 4:
+                return None
+
+            # Remove from both teams (safety)
+            for t in ["A", "B"]:
+                room["teams"][t] = [p for p in room["teams"][t] if p["name"] != player_name]
+
+            # Add to new team
+            player = {
+                "name": player_name,
+                "team": new_team,
+                "position": len(room["teams"][new_team]),
+                "socket_id": socket_id
+            }
+            room["teams"][new_team].append(player)
+
+            # Update positions in both teams
+            for t in ["A", "B"]:
+                for i, p in enumerate(room["teams"][t]):
+                    p["position"] = i
+
+            # Update player record
+            await self.redis.setex(
+                f"player:{socket_id}",
+                3600 * 3,
+                json.dumps({"name": player_name, "room": room_code, "team": new_team})
+            )
+
+            await self.update_room(room_code, room)
+            return room
+
+        try:
+            return await self._with_lock(room_code, _do_change_team)
+        except Exception as e:
+            print(f"Error changing team: {e}")
             return None
 
-        await self.update_room(room_code, room)
-        return room
-
     async def get_player(self, socket_id: str) -> Optional[dict]:
         """Get player info by socket ID."""
         await self.connect()
diff --git a/backend/app/sockets/game_events.py b/backend/app/sockets/game_events.py
index adf289a..8820549 100644
--- a/backend/app/sockets/game_events.py
+++ b/backend/app/sockets/game_events.py
@@ -189,14 +189,13 @@ def register_socket_events(sio: socketio.AsyncServer):
 
         room_code = player["room"]
         new_team = data.get("team")
-        current_team = player["team"]
 
-        # Don't do anything if already on that team
-        if current_team == new_team:
-            return
+        # Use room_manager method with lock to prevent race conditions
+        room = await room_manager.change_player_team(
+            room_code, player["name"], sid, new_team
+        )
 
-        room = await room_manager.get_room(room_code)
-        if not room or len(room["teams"][new_team]) >= 4:
+        if not room:
             await sio.emit(
                 "error",
                 {"message": "Cannot change team. It may be full."},
@@ -204,30 +203,6 @@ def register_socket_events(sio: socketio.AsyncServer):
             )
             return
 
-        # Remove from current team (by socket_id to be safe)
-        room["teams"][current_team] = [
-            p for p in room["teams"][current_team] if p["socket_id"] != sid
-        ]
-
-        # Also remove from new team if somehow already there (prevent duplicates)
-        room["teams"][new_team] = [
-            p for p in room["teams"][new_team] if p["socket_id"] != sid
-        ]
-
-        # Add to new team
-        room["teams"][new_team].append({
-            "name": player["name"],
-            "team": new_team,
-            "position": len(room["teams"][new_team]),
-            "socket_id": sid
-        })
-
-        # Update room state
-        await room_manager.update_room(room_code, room)
-
-        # Update player record with new team
-        await room_manager.update_player(sid, {"team": new_team})
-
         await sio.emit("team_changed", {"room": room}, room=room_code)
 
     @sio.event