A commentator was an individual that provided information and opinions on a subject.
Digger Wells and Brian were cricket commentators during the 1981 Ashes series. During their commentary, the Fifth Doctor's TARDIS materialised in the press box. The two men were unfazed, with Digger replying, "I thought he was here already," to Brian's casual, "The Doctor's here." They allowed the Doctor to remain in the commentary box with them for the remainder of the match. (PROSE: Graham Dilley Saves the World)