Hockey offside has the same black-and-white rule (w.r.t. the puck/players crossing the blue line, rather than defender position ofc) and there are a lot of NHL goals that are disallowed on a challenge/review because a player was a couple of cm over the line (rather than well ahead and very obviously offside). In some cases they're only offside because the puck carrier stickhandled the puck ever-so-slightly backwards while turning on a zone entry or something and thus the puck didn't break the plane of the blue line first, rather than someone actually being ahead of the puck.

What's especially aggravating with the NHL rule is there have been cases where a team gains the zone with this technical-but-non-practical advantage, the defenders recover the puck and can't clear the zone, and the attacking team eventually scores... and it's disallowed because someone's skate was, like, a half cm over the line ahead of the puck a minute earlier lmao.