Green’s Dictionary of Slang

scut v.

[dial scut, the tail of a rabbit or hare; hence that of a farm cart]

(Irish, esp. juv.) to grab a free ride by hanging on to the rear of a vehicle, unbeknown to the driver.

implied in scut the whip!
[Ire]E. Brady All in! All in! 25: Another delight is the practice of scutting behind a car.
[Ire]E. Mac Thomáis Janey Mack, Me Shirt is Black 66: We went to the funeral by scutting on the backs of cabs.
[Ire]R. Doyle Van (1998) 485: Jimmy Sr knew they were scutting on the back, the fuckers.
[Ire](con. 1930s) K.C. Kearns Dublin Tenement Life 99: Scutting was the way you went everywhere. Now if I was going into the centre of town I’d just jump on the back of a lorry passing by.
[Ire]G. Coughlan Everyday Eng. and Sl. 🌐 Scutting (v): catching a ride by hanging from the back of a moving truck and then jumping off.

In phrases

give a scut (v.)

to allow a free ride on the back of vehicle.

[Ire](con. c.1920) P. Crosbie Your Dinner’s Poured Out! 67: The lorry men were the best for giving scuts. They never seemed to mind up to a half a dozen boys on the back of a lorry.

In exclamations

scut the whip!

a warning to a driver that riders are on his vehicle.

[Ire]L. Daiken Out Goes She 12: Boxing the fox, scutting the whip, trespass, fecking [...] Heaven help the poor divil who informs.
[Ire](con. 1920s) L. Redmond Emerald Square 82: Got a free ride up the hill [...] on the back axle of a cab, until some louser shouted ‘Scut the whip!’ and we had to jump off in a hurry.
[Ire]B. Quinn Smokey Hollow 48: Kids hung on the back of the cart. Those for whom there wasn’t room at the back would fall away yelling ‘Scut the whip, scut the whip’ to spoil it for the successful ones.