One of the mysteries of the English language finally explained.
Definition of footguard in English:
footguard
noun
1Usually in plural A body of foot soldiers having a specific guarding role; specifically (usually with capital initials) the infantry regiments of the Household Division of the British army, now comprising the Grenadier Guards, Coldstream Guards, Scots Guards, Irish Guards, and Welsh Guards.
2Any of various types of protective coverings or guards for the foot or feet.
Origin
Early 17th century; earliest use found in Edward Grimeston (fl. 1604–1634), translator. From foot + guard.