What happened to Sam Tatum? Why did that happen? In Chapter 4

Sam Tatum was tarred and feathered because he called Mr. Barnett a liar.

“Tarred and feathered him!” T.J. announced hastily. “Poured the blackest tar they could find all over him, then plastered him with chicken feathers.” T.J. laughed. “Can you imagine that?” “But why?” asked Little Man, forgetting our ploy. This time T.J. did not slow down. “I dunno if y’all’s little ears should hear this, but it seems he called Mr. Jim Lee Barnett a liar—he’s the man who runs the Mercantile down in Strawberry.