Say on my opponent has Machamp and Zangoose. I have Bisharp and Galvantula.
I make my Bisharp use Sucker Punch on Zangoose. However, Zangoose attacks Galvantula instead. So Sucker Punc hdoes not hit Zangoose. However, if Machamp attacked my Bisharp, would Sucker Punch be redirected from Zangoose to Machamp?