can i get baned for throwing teammates into enemy team with tahm?

Potentially yes. I would consider that to be griefing.

You would need to ask a Rioter who handles those kinds of reports to be sure, but I expect that would be considered a reportable offense.

I mean, if you're doing it to put teammates in danger, then yes.

I personally know somebody who did things similar to this, and they got banned pretty quickly.

Yes, you can get banned for that. Also, since it's a gameplay offense that a chat restriction wouldn't help with, the first punishment would be a 14 day ban, then perma ban for the next punishment.

It doesn't matter what game mode you are playing, if you are in match making and you are intentionally doing something to ruin the game for other people. Riot bans you pretty damn quick.