I consider Specialisms in the USR rules to be incredibly flexible. That the rules as written, sparse as they are, leave PC's no choice but to create them and use them in any manner they fit.
A character with the, say, Specialism Agility could try and get an advantage over a heavily armored opponent by striking quickly, or making the opponent off balance before delivering a blow. This appeals to my sense of Sword & Sorcery combat as depicted in the pulps. Indeed, a sell-sword in the gawd awful Game of Thrones books used such a technique against a well armored foe in a one on one challenge to slam his weapon home leaving his opponent gutted and lifeless.
My USR combat rounds are ten seconds, and the action occures simultaneously. PC characters and NPC's characters can use this dynamic to describe what their goals are over the next ten seconds. As the regular rules indicate, characters can roll for a +1 on their actions by successfully rolling against a target number via the use of a Specialism. It is only up to the PC's and the Crypt Keeper to try and put these actions into play through remarkable ideas which are in the spirit of the canon.
The CK can, of course, rule against any application of a Specialism for this +1 bonus and deny the PC this additional roll. In fact, a CK would be best to keep a tight rein on the use of this mechanic, or eventually it will become meaningless through overuse.