Stands in front of royals: guards, at the start, going for their headgear (9)

'start going for their headgear' is the definition.
I can't tell whether this definition defines the answer.

'stands in front of royals guards at' is the wordplay.
'stands' becomes 'bears' ('bear' can be a synonym of 'stand').
'in' indicates putting letters inside.
'front of royals guards' becomes 'ks' (I can't justify this - if you can you should believe this answer much more).
'at' becomes 'in'.
'ks' placed around 'in' is 'kins'.
'bears'+'kins'='BEARSKINS'

'the' acts as a link.