The reason HHH had the biker shorts was because he had a torn groin muscle (or similar) so he had to wear them to prevent it getting worse.
However the biker shorts weren’t enough on their own so to make extra sure when HHH’s pod opened HBK immediately kicked him in the face. HHH then stayed down for the entire match until the end when he ponked Goldberg with the hammer to win.
It was peak Reign of Terror HHH. Not fit enough to participate in a match in any meaningful way, still wouldn’t lose.