  We examine the single-spin asymmetry (SSA) caused by the five-quark
components of the proton for semi-inclusive electroproduction of charged pions
in deep-inelastic scattering on a transversely polarized hydrogen target. The
large SSA is considered to have close relation with quark orbital motion in the
proton and suggests that the quark orbital angular momentum is nonzero. For the
five-quark $qqqq\bar{q}$ components of the proton, the lowest configurations
with $qqqq$ system orbitally excited and the $\bar{q}$ in the ground state
would give spin-orbit correlations naturally for the quarks in a polarized
proton. We show that based on the basic reaction $\gamma q \to \pi q'$, the
orbital-spin coupling of the probed quarks in the five-quark configuration
leads to the single-spin asymmetry consistent with recent experiment results.
