'Queen's gambit declined' ! That gambit, where White starts by moving the Quen's pawn, and any other gambit , is based on the idea that having Black capture the pawn gives White a tactical advantage.'Declined' means that Black has refused to take it. There is no rule that a player must take a pawn or piece and if he forgets to do so and stops his clock or his opponent touches his own pawn or piece , he is stuck without being able to move it.