A cricket pitch was the place where cricket was played. Because it was made mostly of grass and dirt, it was mistakenly called a "field" by those unfamiliar with the game. However, as the Fifth Doctor once corrected Erimem after being shown round the TARDIS' version for the first time, it was definitely a pitch, not a field. (AUDIO: No Place Like Home)
Behind the scenes
Technically, the pitch is just that part of the overall playing surface between the two sets of stumps. It's therefore the place where the bowling, batting, and scoring — but not typically the fielding — occur. However, this point hasn't been made clear in Doctor Who-related fiction.
