In close combat, this is a so-called exchange of blows.
In doing so, you attack an opponent and exchange a few blows with that person.
Rule-wise, that means you roll a comparative test against each other. The person with the most successes applies the excess net successes plus the weapon damage minus the opponent’s armor protection as damage to the other.
For the test, the combat value is used, which is determined by the type of weapon you are using.
Melee
Comparative test of melee combat skills
Net gain + weapon damage of the winner – armor protection of the loser = deduction from the loser’s health
If the winner has used unarmed combat, the damage is instead subtracted from the loser’s concentration.