Theoretical game server DDoS prevention question

I may not understand how DDoS attacks work at this point, but Im just wondering if this would work for a game server?

IF each time a new connection is attempted and the packet or connection type is not similar to that of a normal player, then block the connection?

I dont see any reason for the server to allow connections that are not needed to play the game. Only 1 port would be open. The only downside I see is that the CPU would be put under a lot of stress with large attacks.

But for the most part, wouldn't this work well?

I may be completely wrong and off-base, so i'm just posting here to find out.