lag verb
1 to transport as a punishment, ‘to send over the water’: lagan a gadgie [transporting a man] 19.
2 to accompany 20. etymology: obsolete English lag ‘to transport to penal servitude’; sense 1 collected by and Rev John Baird and Joseph F G S Lucas from Kirk Yetholm Gypsies; sense 2 attested in Shelta note:

Lexicon Balatronicum (1811) Lag a man transported. The cove was lagged for a drag. The man was transported for stealing something out of a waggon.

Canadian Paul Pope (2013) attests this but with the meaning ‘to pee, urinate’.