Soldier and mare crashing into bridge (8)
I believe the answer is:
spearman
'soldier' is the definition.
(I have seen 'old soldier' mean 'spearman' so perhaps 'soldier' could also mean 'spearman')
'mare crashing into bridge' is the wordplay.
'crashing' indicates an anagram.
'into' means one lot of letters goes inside another.
'bridge' becomes 'span' ('span' can be a synonym of 'bridge'**).
'mare' is an anagram of 'earm'.
'earm' placed inside 'span' is 'SPEARMAN'.
'and' acts as a link.
(Another definition for spearman that I've seen is " Parmesan (anag) - old soldier".)