This has happened to me a few times now. I will be playing and see my team mate and then that same team mate will suddenly be from the other team and kill me. How is it possible? I thought it wasn't possible to change teams
22 Answers
He may have left the game and re-joined. If this is the case, and your team was full at the time of re-joining, they will be placed on the opposing team; thus appearing to have 'changed teams'
You can get put on a different team if you have left the lobby and then join the same lobby, or in between games you the game shuffles based on skill level and whether people are in parties. The system tries to make it as even a match as possible, but at times the game can be pretty unbalanced. Hope this helps, if you have any questions let me know!