It always seems to me that there should be guards and, guards. A sentry isn't just a guard, he is a watchout, like a gate guard would never leave his post on pain of severe punishment. You might taunt the gate guard or sentry if you were stupid, but he would never chase you, he would at the most blow a whistle that would summon the regular town guard, and they would chase you for him. Town guards would be lightly equiped, a short sword and maybe a stick for non-lethal jobs, like clearing the tavern of drunks, and wear light leather armour, the gate guards may be more heavily equiped, spears or broadswords and chain, maybe a shield. For serious problems there would always be a troop dressed ready for trouble in the barracks with the full kit, plate, halberds etc.
So there should be a variety of guards differently for a variety of jobs.