More hazardous trail regularly taken by winter sportsperson (7)
I believe the answer is:
riskier
'more hazardous' is the definition.
('risky' can be a synonym of 'hazardous')
'trail regularly taken by winter sportsperson' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'taken by' says to put letters next to each other.
'winter sportsperson' becomes 'skier' (I've seen this before).
The alternate letters of 'trail' are 'ri'.
'ri'+'skier'='RISKIER'
(Other definitions for riskier that I've seen before include "less safe" , "More likely to cause loss" , "More chancy" .)