What is so important about Tom Robindon's physical appearance? What, according to the testimony, does this prove beyond a reasonable doubt?

Tom's left hand was useless, and that is the hand they say he used to beat and bruise her face. The hand had been torn apart by a cotton gin when Tom was young; he couldn't have done that kind of damage......... period.

beat and bruise whos face?

Mayella Ewell's face.