Combat Fumble Chart
If you roll a 1 on a to hit roll, follow it up with a DC10 DEX check (or DCX, X is group's preference). If you fail that then roll on the chart.

An example of the chart (screenshot)

There are a few fumble charts around, and I’ve used a couple before creatibng my own to suit my group’s play style. 

I like how this chart lays the rules out simply while creating situations that don’t just spur the imagination and help liven up combat, but also spark the player’s motivation to try a technique they otherwise hadn’t considered or thought too risky.

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