Wiktionary
on the hop
a. (context idiomatic Ireland English) Playing truant from school.
Wikipedia
On the Hop
On the Hop is a 1967 Australian TV play. It was part of Australian Playhouse and was the first play from actor Michael Laurence.
Usage examples of "on the hop".
Patti's got me in Brussels from Monday night to Tuesday afternoon, with a stop at a London biotech on the hop home.
I think Legolas's bit of news about Gollum caught even him on the hop, though he passed it off.
If only term had not caught me on the hop again, I should have revised the whole –.