Following last week's post on adapting Vancian magic, here's a general response to the recent discussion on fighters in early D&D, especially customisation. It's an even simpler suggestion.
Before each attack, and consistent with this summary, the player can very briefly state how exactly the fighter makes the attack, what one additional effect the fighter aims to achieve etc.
For example, a fighter whose master emphasises positioning may declare a strike is also intended to turn the foe, or pressure an individual back, or draw one opponent off.
If the attack succeeds by a margin of a quarter the range of the die or more (e.g. 2 if a D6, 5 if a D20, or 25 if a D100), the usual result and the stated effect are applied. If the attack fails by this margin instead, the DM / GM may apply a relevant adverse effect.
You can tinker with effect power, and make it higher if you already use a similar system without a margin. It might be decided a given effect needs a further check of some kind.
This gives a player explicit scope for customisation and creative input in general combat, and there's automatic improvement as character skill rises. It could be used as a more overt mechanical basis for related interactions like shaming, angering or persuasion.
It could work in wargaming too, even without a referee if the players agree effects first.