Here is a post I made in the comeback thread, I'll repost it here because it's relevant. Hope this helps:
The reason why comebacks don't happen too often is because most people do not understand the basics of the game.
If the enemy caps your portal flag.... there's really no point trying to sit back and wait for it to uncap, so you can grab it. A competent team will TP before the lock expires, recap, and repeat. They can do this forever, with nothing you can do about it. Now, you might say "yeah but i can interrupt" which you can. Except I'll fake out to trick you. I'll use my tp, you see my character sitting still trying to cast something and you want to cancel it, I cancel it immediately, due to lag I can cancel my TP faster than you can interrupt, leaving you on cooldown, then I cap your flag . Conversly, a good team will see that the opponent is in your base and there's no point - so now it's time to cap their flags and lock them back. And if they don't understand the basics they will leave your base - retreat - and try to defend their stolen portal - then you get your portal back .
The main thing is this, I've played countless games with pugs, I'll cap both of the enemy portals, my stuff is on cooldown or I ran out, and my allies will not tp and relock. This can cost you the game. I've also played games where my cit is almost dead, someone buys cit health, we grab both of their flags and lock them, enemy leaves our base, we get ours back, and we re-lock theirs until the game is over and we win.