Ok ok, he's literally fueled with "Nakama power" ...
That aside, I believe that "straight" here is ambiguous, as it could mean both the straight punch, but i also understood it as the "fastball" pitch as the japanese call them "straight" if i remember correctly from the Ace of Diamond. I imagine it's the same for baseball in asia in general, even in Korea. (i know that they also call it "straight" in Taiwan too so...). Could be wrong though.
I think it would make more sense considering the fact that these baseball nutjobs only speaks with baseball terms
....Actually...now that i think about it, he threw a right "straight" (the punching motion) which resulted in a "straight" (the fastball pitch) so both meanings work.... Well played author.