The hero of the hour points out that there was nowhere to hide, no quick way out, and when the shooter stopped to reload (where was he keeping his spare magazine, since he was naked?), he saw a chance to intervene and took it.
Quick thinking and brave, yes. Unwilling to tackle the naked guy, also yes.
"Sure, I'll grab a scorching hot gun barrel and yank it away from him, but... dude's naked. Nuh-uh."