Yarn's covering new golf mats (7)
I believe the answer is:
tangles
'mats' is the definition.
('tangle' can be a synonym of 'mat')
'yarn's covering new golf' is the wordplay.
'yarn's' becomes 'tales' ('tale' can be a synonym of 'yarn').
'covering' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'n'+'g'='ng'
'tales' enclosing 'ng' is 'TANGLES'.
(Other definitions for tangles that I've seen before include "Sent gal (anag.)" , "Knots" .)