A beamer was a type of delivery in cricket that the Fifth Doctor didn't "normally bowl", but which he nevertheless once used to disable a grandparent scorpion threatening to eat Rupert Von Thal. Nyssa punned that the scorpion had been "bowled out". (AUDIO: The Boy That Time Forgot)
Behind the scenes[]
Unremarked in the story, though certainly implied by sound effects, is that a beamer is a bowl which does not touch the ground before hitting its target. This makes it a type of full toss. However, a beamer is fast and intentionally bowled above the waist of the batsman. The bowl is illegal in cricket as it poses an unacceptable risk of injury to the batsman, which is why the fair play-minded Fifth Doctor would not have "normally" bowled it. By contrast a full toss is not illegal, because it is aimed below the batsman's waist.