OOPS!
As an air cadet I flew my Flying Scholarship at Luton in 1961, in Tiger Moths G-AOGS and AOZH. As cadets, after careful instruction we swung props on the Tigers and any visitors (would we be allowed to so today?!). The visiting Miles Messenger below was swung by the pilot with no-one aboard and no chocks. With full power it charged off at speed across the grass, gyrating in large circles for several minutes, defying the valiant efforts of the fire crew, while we rushed to push our Tiger round the corner. Eventually, after avoiding a row of brand new Jet Provosts and the control tower, it hit a marker-board and then caught its wingtip on a hedge outside the flying club and embedded its nose on the club bar with the propeller shattering all around. The bar was fortunately unoccupied and no-one was hurt.
See photo here, I can't post links yet.
www.pprune.org/g/picture/13197522