Fighter A, who is winning 2:50 seconds of the round by slightly outpointing Fighter B with jabs and mini crosses but nothing to near stop the fight or cause a knockdown. In the last 10 seconds Fighter B lands a massive overhand causing Fighter A to stumble hard, a very damaging shot that stuns Fighter A bad. Round ends. Who won? Boxing fans have had a clear difference in scoring fights, who do you think should've won this round?
How bad is he stunned though? Parker did it a lot without stunning Joyce. You also have the Canelo vs GGG type fights orHagler vs Leonard. All in all it depends.
I don't believe a round of technical domination full of decent but not hard punches landed can or should be wiped out by a single heavy blow in return. But I totally understand the opposite POV. It's just not how I think a fight should be scored. Should you be able to win a fight with (theoretically at least) seven hard punches?
Probably fighter A. I judge rounds by having a constant tipping scale in my head. Kind of like the guy doing the best work gains 1 point per second then the guy with the most points at the end of 3 minutes gets the round. occasionally legit draw rounds are totally viable however due to the nature of scoring they are never given, these kind of rounds happen in good matchups where there is likely going to be another close or draw rounds, so I will give them out equally, Pacquiao Marquez for instance. Watching on TV it's extremely easy to score rounds although the commentary and crowd can be very biased and fan scoring in RBR's makes you want to gouge your eyes out.
Fighter A gets rocked, stumbles and clearly got hit by the biggest punch out of the entire round, does duration or impact win the round?
Obviously, we would all need to see the round to judge everything but, going strictly by your hypothetical, I would take fighter A. However, the problem is you mentioned what Fighter A was doing for the first 2:50 but not Fighter B. Assuming B was getting in his share of shots during the first 2:50 I would switch to fighter B.
If B is doing something for the first 2:50 then B, but if it's one sided for the first part then A. I think this is where ring generalship and defense comes in. Was B using ring generalship over the last minute to set up that shot? Were the small shots getting defended or landing cleanly?