How to other players view the individual Kills & Deaths

Turn to look at your Medic and pay attention to the healing beam. If you see yellow streaks on the beam, and you see glowing yellow lights on the gun itself (without custom skins), it's a Kritzkrieg. If the Medic's backpack appears different than usual, and you see yellow and blue/green streaks on the beam, it's a Quick-Fix.

You can also watch the Medic's charge rate. If it's going up pretty quickly, chances are it's a Kritzkrieg or Quick-Fix. After a while of observing and comparing charge rates for all the mediguns, you'll be able to tell the difference at a glance.

In order to avoid it I suggest to not try entering more than once in the door of specified team, if the first time fails selected random.

Anyway, if it happens that you got stuck, you can easily recover from this bad situation by opening console and write

retry

Retry command force a server reconnection and you access again the team selection screen. Sometimes, on busy servers with many people try connecting, this command causes to lose the slot.

For this reason, as suggested by @Dave McClelland in comments, is preferable use the command

spectate

because it fix the problem without forcing a re-connection.

If you really want to join RED or BLU team and reduce the probabilities to trigger that annoying behavior, I suggest to wait that half or more users on the server choose their own team, and then try enter your desired door.