In the game manual on page 36 it says
"Display tackle zones T"

This is one of the in-game shortcut keys. Pressing T actually does nothing. I think the same problem has been in every Blood Bowl version. I tried pressing every key (in case this is another AZERTY bug from way back) but nothing specifically displays the tackle zones (I know about G).

You even have the T key advertised in one of the messages that appear when a game is loading. You might want to look into this? Maybe drop the message and change the manual? Pressing G already shows the tackle zones at least somewhat. I don't know if you originally meant for T to do something different.