IF A TEAM MATE ATTACKS YOU DURING A 3 ON A TEAM GAME AND DOES NOT REPLY TO YOUR MESSAGES ASKING WHY HE'S ATTACKING, IS THERE SOME SORT OF SITE PENALTY FOR THAT PLAYER?

IS BLOCKLIST THE ONLY OPTION?

Generally, yes, there's no site penalty for bad in-game behavior (except for things like harassment/language/etc.). Usually your best bet is to be more selective about whom you play with (this includes the Block List but also using features like Quickmatch or Clans to find players who're less likely to do that). And not to sweat the boot/surrender (the occasional boot isn't a big deal) if it helps you get out of a game like that.

It's unusual for someone to backstab a teammate in a 3v3 game, though. Could you link the game here? If you're lucky, there could've been some multi-account shenanigans going on.

PS: Please toggle off Caps Lock. It reads like you're yelling.

No penalty because attacking a teammate is within the rules of warzone gameplay (unless the game creator has specified that as a rule, but they would have to enforce any penalties) While blacklist is an option, you could simply stop playing with person to help them get the message.

If you part of a clan and you are fellow clan members, you can protest to the clan leaders to help you settle the dispute.