In ordinary conversation, you sometimes hear phrases such as "call for an offside", "scream for an offside", etc. So it does exist as a noun.
However, in the contexts where you might expect a noun, it's more common to use a phrase such as "he was offside", "he was in an offside position", "he was booked for being offside", "an offside offence", etc.
All the best,
- For Teachers