Measure shields for some infantry regiments (4,6)
I believe the answer is:
'measure shields' is the definition.
The definition suggests a singular noun which matches the answer.
'some infantry regiments' is the wordplay.
'some infantry' becomes 'foot' (foot soldiers).
'regiments' becomes 'guards' (I am not sure about this - if you are sure you should believe this answer much more).
'for' acts as a link.
Can you help me to learn more?
(Another definition for foot guards that I've seen is " British infantry regiments".)