Upset Irish winter sportsman? That's more dangerous (7)
I believe the answer is:
Here is my best explanation:
'more dangerous' is the definition.
('risky' can be similar in meaning to 'dangerous')
'upset irish winter sportsman?' is the wordplay.
'upset' is a reversal indicator.
'irish' becomes 'ir' (abbreviation).
'winter sportsman?' becomes 'skier' (I've seen this before).
'ir' reversed gives 'ri'.
'that's' acts as a link.