Some maths to give a broken leg support (7)
I believe the answer is:
algebra
'some maths' is the definition.
(algebra is a kind of maths)
'give a broken leg support' is the wordplay.
'give' means one lot of letters go next to another.
'broken' indicates an anagram.
'support' becomes 'bra' (a support for the breasts**).
'leg' is an anagram of 'lge'.
'a' next to 'lge' is 'alge'.
'alge'+'bra'='ALGEBRA'
'to' is the link.
(Other definitions for algebra that I've seen before include "Branch of maths using letters and symbols" , "'Branch of mathematics, uses letters and symbols (7)'" , "Part of the maths syllabus" , "branch of learning" , "Symbolic maths" .)