LONDON — When a man has been the best of his kind, and then is laid idle by injury for eight months, the pain of withdrawal becomes cerebral rather than physical.

For David Villa, the relief at coming back on Sunday was beyond words.

He entered the field late in the game between Barcelona and Real Sociedad and was given a standing ovation by 75,000 at the Camp Nou. When he then scored a trademark David Villa goal 10 minutes after joining play, his celebration was preplanned and personal.

He stripped off his scarlet and blue jersey, revealing a black shirt imprinted with a photograph of his wife and their two daughters, and the words: “Imposible sin vosotras” — Impossible without you.

Inevitably, the referee showed him the yellow card. The sanction, carrying the same weight of punishment that is issued to a player who threatens the livelihood of another with a reckless foul, shows how insensitive the sport sometimes is to its most important people, the participants.