Combat in a fantasy roleplaying game should be more than simply lining up and trading blows. However, many tactical subsystems end up being far too specific, too complex to remember or too fiddly to use in a fun and engaging way, and a dull rule is a rule ignored.
Here is our first take at increasing the options in OSR combat: Knocking enemies backwards:
Any character may forego one of their melee attacks to knock an opponent out of the way. They must be in melee range of course.
Knocking an opponent away requires the same roll used for knocking open a door (in the system of use). In "Classic" games, this is usually a D6 roll of 1-2 modified by Strength.
If achieved, the opponent is knocked backwards. If exact measurements are wanted (for example, when fighting on a bridge), the knockback is 1D6 feet.
The recipient of a successful knockback also suffers a -2 penalty to their next attack roll.
Otherwise, simply assume it's enough to enable someone to slip through or past the combatant, or even disengage from melee. DM discretion is obviously needed for specific situations.
A character with multiple attacks may attempt multiple knock backs on the same or different targets.
Targets larger than the attacker can be knocked back, but it is less likely. On a successful roll, the target is "staggered", inflicting a -2 to their next attack roll. The attacker immediately rolls again, and on a second success, the target is also knocked back the normal distance.
The DM should judge when a target is too large to be knocked at all.
Knocking back a smaller target is not any easier (they're slippery little blighters) but the knockback distance is increased to 2D6.
Give it a shot next time you game, and let me know how it fares!