I went back and checked the Kawamura and Kabaji doubles match and found this:
Now it's impossible to say which team say "It's match point" but since Kawamura is saying "This isn't going to work" I assume it's not his team that gets the match point. They were surprised when they got the badge, so it sure doesn't look like it was Kawamura/Kabaji's match point.
But Kawamura just hit someone with the ball! Tennis rule says if you hit the player with the ball and they didn't return it, it is a point for you! I guess it could've been double match point for the opposing team but it seems pretty clear that the Hado 108 is a desperation attempt at match point because it was the first time it happened (using Hado 25 to save a match point seems like a pretty bad idea given what they've already observed).
So in conclusion the power players must not play by standard tennis rules. If you hit someone with a power shot but it didn't cause any injury, it must count as a point against you for your failure as a power player.
This also explains why Byodouin used his hand to catch Ryoga's return, a move that'd be completely useless in normal tennis (he'd lose the point no matter what), but he'd score in Power Player Tennis.
I think its clear as day that Kawamura/Kabaji pair were not at Match Point.
The only points they took were the two occasions that they hit Ban in the stomach with their shots.
And then again with the 108th Hadoukyuu.
I think Konomi showed us that 108th Hadoukyuu is in fact a shot at the HS level. Since Ban was gonna swing for it but he moves his arm out of the way.
That shot gave the impression it was beyond what Ban could handle.
All it means is that in not just Power Play matches, but any match, if you can KO your opponent you win the match.
Tooyama took out Ibu from just 3-0.
Gin and Kenya took out Kamio and Tetsu at just 4-0.
The Power Players do play be normal rules. But they tend to avoid long drawn out matches.
The only way that sequence could make sense if the other team had a double (or triple) match point because hitting someone on the stomach with them not returning the ball should always be a point for you regardless of how much or how little damage was done, because the ball wasn't returned.
But then using Hado 25 to save a match point wouldn't really make much sense given Kawamura is in theory capable of 108. There was no indication that they were at a match point situation before hitting Ban and POT is usually pretty consistent about telling you when they're at match point
So the only way that scene can make sense is if hitting your opponent with a power shot without damaging him counts against you!
At any rate at the end it's pretty clear that K/K team lost the match but won the power battle, and I always assumed the other team gave them their badges because they didn't want to die.
Since looking at how happy Ban was made it clear that he wasn't losing.
Secondly, Kawamura tried a power shot, Ban felt it but it didn't hurt him at all. It doesn't imply that Kawamura was winning. As the readers it's kinda obvious that they were losing.
Ban didn't get a point from it, but Date and Ban were already at match point.
At the same time, Mutsu/Mutsu were about to finish off Niou/Oishi if you remember Oishi and Niou fretting they it could be over soon,
And the same with Momo VS Taira/Hara, where Momoshiro had to throw everyting into his BJK since it can be assumed Hara and Taira were about to finish things off with him too.
So again, Power Play matches play by normal rules.