The defense's challenges to this evidence

Atticus basically factually dismisses all the prosecution's claims. These include:

-Tom's lame left hand compared with the angle and severity of Mayella's wounds.

-The evidence was only hearsay.

-Bob didn't call for a doctor.

-Mayella's very stilted and conflicting testimony.

-It is not lost on anyone where so many children belonging to Bob might have come from. (yuck!)