Mudball

aka mud ball

Illegal since 1920. Mud is packed onto one side of the ball, loading and roughening it so the ball flies off balance and breaks erratically. The twist: rubbing every new ball all over with special mud is required and legal; piling it on one side to make it move is what's banned.

Schematic baseball cover. This pitch has no filed seam geometry yet — the grip and shape below are sourced in words, not measured here.

The grip

Mud is worked into one hemisphere of the ball, loading and roughening that side while leaving the other clean.

Reputable analysisSABR — The Spitball and the End of the Deadball Era (Feb 1920 Joint Rules Committee ban; Chapman post-ban; named freak pitches incl. mud/shine/emery)

What it does

The mud-loaded side throws the ball's weight and surface out of balance, producing erratic break — the same family of asymmetry the emery and shine balls exploit.

Reputable analysisSABR — The Spitball and the End of the Deadball Era (Feb 1920 Joint Rules Committee ban; Chapman post-ban; named freak pitches incl. mud/shine/emery)

What it really is

Named explicitly in the February 1920 ban alongside the shine, spit and emery balls. The irony is sharp: rubbing every new ball all over with Lena Blackburne rubbing mud is mandatory and legal under MLB Rule 4.01(c) to dull the gloss — it is loading mud onto one side to make the ball break that crosses the line.

Reputable analysisBaseball rubbing mud — Wikipedia (Lena Blackburne mud mandatory/legal under Rule 4.01(c) to dull gloss)

Who throws itDeadball-era spitballers (broadly attributed)

Basic file

This pitch has a sourced one-line grip and movement and an honest explanation — not yet a filed specimen with authored grip geometry and a full craft chapter. A fuller breakdown is coming. Sourced, not corrected.