diff --git a/models/player_model.py b/models/player_model.py
index 100cb39..aa85389 100644
--- a/models/player_model.py
+++ b/models/player_model.py
@@ -5,6 +5,15 @@
 - `PlayerRequestModel`: Represents player data for Create and Update operations.
 - `PlayerResponseModel`: Represents player data including UUID for Retrieve operations.
 
+Design decision — single request model vs split models:
+    A single `PlayerRequestModel` is intentionally shared by both POST (Create)
+    and PUT (Update). Per-operation differences are handled at the route layer
+    rather than by duplicating the model:
+    - POST checks that `squad_number` does not already exist (→ 409 Conflict).
+    - PUT checks that `squad_number` in the body matches the path parameter
+      (→ 400 Bad Request), ensuring the request is unambiguous. The path
+      parameter is always the authoritative source of identity on PUT.
+
 These models are used for data validation and serialization in the API.
 """
 
diff --git a/routes/player_route.py b/routes/player_route.py
index 4e50d66..631e511 100644
--- a/routes/player_route.py
+++ b/routes/player_route.py
@@ -199,9 +199,14 @@ async def put_async(
         async_session (AsyncSession): The async version of a SQLAlchemy ORM session.
 
     Raises:
+        HTTPException: HTTP 400 Bad Request if squad_number in the request body does
+        not match the path parameter. The path parameter is the authoritative source
+        of identity on PUT; a mismatch makes the request ambiguous.
         HTTPException: HTTP 404 Not Found error if the Player with the specified Squad
         Number does not exist.
     """
+    if player_model.squad_number != squad_number:
+        raise HTTPException(status_code=status.HTTP_400_BAD_REQUEST)
     player = await player_service.retrieve_by_squad_number_async(
         async_session, squad_number
     )
diff --git a/tests/test_main.py b/tests/test_main.py
index 6ac99be..9ed2f73 100644
--- a/tests/test_main.py
+++ b/tests/test_main.py
@@ -234,6 +234,20 @@ def test_request_put_player_squadnumber_existing_response_status_no_content(clie
     assert response.status_code == 204
 
 
+def test_request_put_player_squadnumber_mismatch_response_status_bad_request(client):
+    """PUT /players/squadnumber/{squad_number} with mismatched squad number in body returns 400 Bad Request"""
+    # Arrange
+    squad_number = existing_player().squad_number
+    player = existing_player()
+    player.squad_number = unknown_player().squad_number
+    # Act
+    response = client.put(
+        PATH + "squadnumber/" + str(squad_number), json=player.__dict__
+    )
+    # Assert
+    assert response.status_code == 400
+
+
 # DELETE /players/squadnumber/{squad_number} -----------------------------------