Rule-Set Differences: ACF vs FMJD / WCDF
Why the rules differ
Different traditions grew up around different boards, so several official rule sets exist. The two most common reference points are American or English-style checkers, used by bodies such as the ACF and the WCDF, and international draughts under the FMJD. Knowing which version you are playing matters, because the same move can be legal in one and impossible in the other.
Do men capture backward?
This is the single biggest difference for beginners. In official American and English draughts, ordinary men capture FORWARD ONLY; an uncrowned man can never jump backward, no matter what. In international draughts, ordinary men may capture both forward and backward. Get this wrong and you will either miss legal jumps or attempt illegal ones.
Flying kings, or not
In American and English checkers the king is not a flying king: it moves and captures one square at a time, just in both directions. In international draughts the king flies, sliding any distance along an open diagonal and capturing from afar. The flying king is so strong that promotion changes the whole character of the 10×10 game.
The maximum-capture rule
All these versions make capturing mandatory, but they differ on which capture. In American and English draughts there is no maximum rule: if several jumps are available you may choose any of them. In international draughts you must take the capture that wins the most pieces. So one game lets you pick your favorite jump while the other forces the greediest one.
Board size and casual rules
American and English checkers use an 8×8 board with twelve men a side; international draughts uses a 10×10 board with twenty men a side. Beyond the official codes, many people play a relaxed or casual rule set that drops the strictest requirements, often allowing you to skip a capture, ignore the must-jump-the-most rule, or let men jump backward, simply to keep friendly games easy and forgiving. There is nothing wrong with casual rules, just agree on them before you start.