Its quite simple really after a certain point people should no longer be able to join the game. And there are several points.
1. After the first 5 minutes of the game.
2. After and objective has more than a 1 score difference in Assault or Flag.
3. If and objective is tied but one team has a set amount more kills than another.(Basically if a team is padding their stats on another team, players should not have to Jip into this situation.
4. If a one team is ahead by more than 20 kills in a slayer(Big team) 10 kills in normal playlists.
Just these few things will help a lot. Nobody likes to join into an automatic loss.
Yeah, that's basically what happens now. In fact, I believe (without looking at the code -- famous last words) that every game mode has its own set up rules that tell the matchmaker when to stop backfilling.
But even under those conditions, you'll get rare cases of backfilling into a quick loss.
- CTF match starts
- 2 minutes go by while teams are getting a feel for each other
- Team 1 scores
- Player A leaves the match.
- Rules say it's still OK to backfill, requests 1 more player.
- Player is found and begins loading
- Team 1 at this point has become organized and "figured out" Team 2, they quickly score again
- Player J loads into the match at this point, it's 2-0
- Team 1 quickly scores again.
In this sequence, at the time Player J was requested, everything looked fine (only 1 point, only 2 minutes in, etc.), but things "escalated quickly" while the player was still loading in.
It's uncommon, but can and does happen.