If you went by the Demographics in the DMG, a 50 commoner Thorp would contain a sprinkling of higher level characters, mostly in the 2nd to 3rd level range. Out of 50 1st level nobodys, you'd have about 45 commoners, 2-3 Warriors, and maybe one expert, aristocrat, and adept. The Highest level Warrior, assuming average rolls, would be a 4th level Warrior with 2 2nd level assistants.
So they'd have about a half dozen trained defenders on hand, but nobody really impressive. Human Warriors with scale mail, sheild, and shortspears would be AC 16, HP 5 At +2 1d6+1. Their choice of bonus feat would be a wildcard that could lead to some impressive advantages. (Alertness, Toughness, and Wpn Focus being great feats for low-level guards)
1vs1, A human guard could could manage 5% advantage in hitting, but are hampered by slower movement speed, no darkvision, and don't have the Orcs "confirmed kill" advantage, which is suprisingly huge in these skirmishes. Funny really, because I always thought lightly armored Orcs with Falchions was overkill vs other mooks, but it's actually leads to a very impressive "One shot, One Kill" strategy. You know, as long as they aren't getting shot at with archers. Another reason to stay away in daylight.
Turning to the MM, a 20 strong Warband will include 20 Orc Warriors, already enough to possibly overwhelm the warriors and commoners in a straight up battle. Throw in the 2 3rd level Seargents, and 1 3-6th level Head Honcho, and things are looking pretty grim for the humans. Attacking under cover of night, there is really almost no situation where the Orc warband could fail to take this village. At worst, they may take more casaulties then they expected.
At best...a single 3rd level Orc Barbarian with Cleave is pretty much a one-orc peasent killing machine. It would take a considerably larger force of commoners to hold these Orcs off, I think.