For example, let’s say that your game server sends out a position update every 20 milliseconds, and it does this all over an individual TCP connection to each player.
If one client starts to lag, the server can notice that those updates are piling up on that client’s send queue, and stop sending updates to that client. Then, as soon as the client’s buffer starts to be consumed, it can send whatever the most recent state is, which compensates for the most serious problem of TCP with respect to real time protocols, which is that stale updates clog the connection and leave a player experiencing some temporary packet loss far out of date.