Attacking with a melee weapon in to a grapple is more a matter of luck than skill, as there is an equal chance of hitting each grappling combatant. When we were attacking the grapple-happy Marrowbreakers we had to check to see if we hadn't hit an ally by mistake. With Tal in a grapple the DM had many occasion to ask us to 'Roll to see if you hit the Marrowbreaker or Tal.'
'Okay, if I roll high I hit it', or, 'if I roll high I hit the monster', came the reply.
In each case we had to clarify 'Who do you mean, Tal or the Marrowbreaker?' and there was much rejoicing. This probably irked Tal a bit, and if it didn't we must have pushed him over the edge when the second Marrowbreaker grappled with Dexter.
'Roll to see if you hit the Marrowbreaker or Dexter.'
'Okay, if I roll high I hit it.' <rolls die>
'... Wait, aren't you going to ask who he means?' asks Tal.
'Nope, it's pretty clear he means the Marrowbreaker to me.'