QuarkFieldPsi is the name of a fermionic field.This is just a name with no functional properties. Only typesetting rules are attached.
QuarkFieldPsi\psi
QuantumField[QuarkFieldPsiDagger] . GA[\[Mu]] . CovariantD[\[Mu]] . QuantumField[QuarkFieldPsi]
ExpandPartialD[%]\psi ^{\dagger }.\bar{\gamma }^{\mu }.D_{\mu }.\psi
\bar{\gamma }^{\mu } \psi ^{\dagger }.\left(\left.(\partial _{\mu }\psi \right)\right)-i T^{\text{c19}} g_s \bar{\gamma }^{\mu } \psi ^{\dagger }.A_{\mu }^{\text{c19}}.\psi