Golf spectators are used to taking one in the head. But they rarely take one where this fan took it.

According to the description of the YouTube video from the PGA tour:

In the second round of the 2014 TOUR Championship by Coca-Cola, Rory McIlroy’s tee shot goes left into the trees and somehow lands in the pocket of a spectator on the par-4 14th hole. McIlroy would go on to two-putt for par.

The fan was allowed to keep the ball. From the video it appears that was because no one wanted to retrieve it.