Some of these judges just don’t know how to score a fight. Vargas might have been well up midway, but Ball won 2 rounds 10-8 and you couldn’t give Vargas any of the rounds in the second half of the fight. Impossible for him not to lose.
Yes, the knockdown in the 8th was debatable, but once it’s given, it’s given.
Having said that, the crowd shouldn’t be booing him. He never made the decision. And he’s a very decent fighter.