I am used to check the scoreboard from various other games and that habit just kinda followed me to here. Every other (possible) reason to press TAB has already been mentioned.
Another game handled this by adding a key which you had to press while holding down the tab-key in order for the input on that screen to change to "menu" mode.
This idea has already been mentioned thrice in this thread and I approve of this.
However, I do feel as if the "mute"-thing should really be seperated from actual blocking. As said before if some chill guy plays music and you don't want to hear it, you block him, but then this guy can't even communicate with you per chat anymore either and this can turn into a potentional lack of teamplay. (Does somebody hear your voice commands when said person blocked you?)
Example:
He/She is your captain, the other 2 want to hear the music, but you can't stand it -> block. Congratz, since you are not listening to your captain anymore, you might as well leave the match! (Unless you know what you are doing and the captain isn't doing some special tactics that nobody gets)
Another thing I don't like is that blocking actually removes the person from your friend list. If music guy is playing music again, but you don't want to hear it, but still actually don't want to remove him from your important friend list, mute him instead of blocking him.
But then again, this is only a thing for lazy people, since you can just re-add him or tell him to stop outright and as a friend he might actually listen.
This game is still awesome.