Balks, step by step.

How the umpire checks it

1. Start with runners on base. Without runners, there is no balk call.
2. Watch for an illegal action such as starting and stopping improperly, failing to step directly toward a base on a pickoff, or simulating part of the delivery without completing it.
3. If the illegal motion happens, the umpire marks the balk.
4. Then judge the outcome of the live action in codes where play continues: did all runners and the batter-runner safely get at least one base?
5. If not, enforce the balk award. If yes, the play result can stand instead.

Details fans miss most

• It is about deception limits: pitchers cannot mimic one action while really doing another once engaged with the rubber.
• Not every balk kills the play instantly in practice: some levels let action finish before deciding whether the award is still needed.
• The step matters: on pickoff tries, where the free foot goes is often the whole ruling.
• Runner awards are the point: the law is protecting baserunners from unfair deception, not punishing style alone.

The legal position establishes the pitcher's choices

From the set position, the pitcher ordinarily brings the hands together, comes to a complete stop, and then either delivers, steps off correctly, or makes a legal step and throw to a base. Beginning the delivery commits the pitcher to continue without an illegal interruption. From the windup, a different sequence is permitted, but the pitcher still cannot make motions naturally associated with the pitch and then fail to deliver. Before judging a twitch or turn, identify whether the pivot foot is engaged with the rubber and which pitching position the pitcher has assumed.

Several different acts protect the same runner expectation

A balk can result from failing to stop in the set position, starting and stopping the delivery, making a quick pitch, dropping the ball while on the rubber, separating the hands and rejoining them, or feinting where the rules do not permit it. On a pickoff, the pitcher generally must step directly toward the base before throwing; throwing to an unoccupied base is restricted unless making a play. The full official list matters because no single shortcut—such as “the pitcher fooled the runner”—captures every violation, and a deceptive move can still be legal when performed within the permitted mechanics.

A pitch or throw can produce a better result

Under professional rules, a balk is normally delayed when the pitcher delivers or throws so the immediate action can finish. If the batter reaches first and every runner advances at least one base, the play can stand and the balk is disregarded. If that condition is not satisfied, time is called and each runner receives one base from the base occupied when the balk occurred; the pitch generally does not count. Amateur codes can use different immediate-dead-ball procedures, so the same illegal movement may look different after the umpire signals it.

An illegal motion may have a different name

A balk protects runners, so professional baseball does not call one with the bases empty. The same quick pitch or prohibited delivery action can still violate another pitching rule and be penalized as an illegal pitch, often producing a ball. With runners aboard, that conduct may instead meet a listed balk provision. Always establish the base state first, then identify the pitcher's position and action; copying a balk signal from a runners-on situation can give the wrong ruling in an empty-base plate appearance.

"He never threw the pitch, so why is that a violation?"

Because the balk rule controls the pitcher's movements before release as well as the throw itself. Once the pitcher begins certain motions, the law restricts how he can stop, turn, or feint.

Source material

• MLB Balk
• MLB Rules Glossary
• Little League Rules, Regulations, and Policies