Is there any indication you're joining a match in progress though? I joined a game today and was looking at a big red DEFEAT in literally three seconds. I barely left spawn. They literally threw me in at the very end. It's pretty shitty to have to take that on the nose.
You can only tell if there's no team setup. And also when the match ends, there's the backfill XP bonus. You don't get the loss from defeat tho so use it as practice if possible.