The Fork
How to spot it: look for enemy pieces (or the king and a piece) that share a square your knight can jump to, or that line up on a rank, file, or diagonal. A check that also hits a loose piece is the most common fork of all.
How to recognise it in a game
Before calculating moves, scan for two valuable enemy targets that can be attacked from one square. Knights make this especially easy to miss because their attacks do not follow a line. Checks, attacks on the queen and attacks on loose pieces deserve priority.
The common calculation mistake
Do not stop when you see the fork. Confirm that the forking piece can reach the square legally, that it cannot simply be captured, and that both targets really matter. A fork that loses the attacker for nothing is only a visual pattern, not a tactic.
How to defend against it
When defending, keep valuable pieces from sharing a knight-fork square and notice checking forks before making a natural move. If a fork is unavoidable, look for an in-between check or a forcing move that changes which target can be taken.
Now spot it yourself
A real position: find the move. This is exactly what the drills in the app do, banded from beginner to expert.
How this lesson is made: this public explanation comes from the authored Strong Squares curriculum. Automated checks protect its chess data, source fields and learning flow. Independent chess-editor approval remains part of the private-preview release process. Read the teaching method.