Hitstop
Hitstop is a tiny freeze on the frame a hit connects: both fighters hold their pose for a few frames, so the blow feels solid.
Also called hit stop, hit pause, hit lag.
Hitstop, also called hit stop or hit pause, is a pause of a few frames at the moment of contact. The attacker and the target hold still while the rest of the world carries on, and the blow reads as if it bit into something. Without it, hits tend to feel like they slide off.
How long should hitstop be?
Shorter than you'd guess. A few frames at 60 frames a second carries an ordinary hit, and a longer freeze starts to read as lag, especially in a fast fight with dozens of hits a minute. Give heavier blows a little more and light or ranged ones almost none.
Hitstop in Mytheria
A sword hit holds for 4 frames, about 67 milliseconds. Heavy weapons hold for 5, a harpoon thrust for 3 and ranged weapons for 1, and a kill adds a few frames more. Almost all of the screen shake happens inside the freeze, so your eyes can keep track of the fight.
The freeze never pauses the game. Only the two fighters' drawings hold their pose, so in co-op nobody else's game stops while you land a combo, and players who turn on Reduced motion skip it entirely.
The full post, with clips and demos How to make combat feel good