Single Transverse-Spin Asymmetry in $p{p}^{\uparrow }\to \pi X$ and $e{p}^{\uparrow }\to \pi X$

Cross section formulas for the single spin asymmetry in $p^\uparrow p\to \pi(\ell_T)X$and$e p^\uparrow \to \pi(\ell_T)X$ are derived and its characteristic features are discussed.