The crimewave happens in a small town with only one sheriff dealing with the mess. Any help would be too far away.
The hero finds himself in the wilderness with no one else around to help.
All the other experts who could potentially help the situation are dead, leaving a single hero to save the day.
A Failure Hero struggles to do anything right during the crimewave while the other officers deal with the criminals.
A single villain shows up to attack while every cop or soldier in the area come in to fight him off.
Subverted: A cop goes in to fight the crimewave but has several partners with specialized talents to back him up when the situation calls for it.
Double Subverted: The partners are all killed and the hero is left alone.
Parodied: Da Chief sends all of his officers out to confront the crimewave, only for each and every one of them to be unavailable for goofy reasons: one is too sick to come to work, one ran off and married his girlfriend, one turned and ran when he saw the large number of bad guys, one gets killed in a Bloody Hilarious way, etc., leaving one cop. Chances are, it will be the dumbest guy on the force.
Zig Zagged: Only one officer seems available to fight the crimewave but it turns out, the rest of the force were going undercover to stop the crimewave from within, but after they are killed, the hero is alone.
Averted: The crimewave is stopped by a crack team of experts who all have a role to play in stopping the bad guys.
Enforced: The writer wants to show how Bad Ass the hero is by showing how incompetent the other cops are, so he can save the day by himself.
Lampshaded: "Why is it, I'm always the only one available to stop the bad guys?"
Invoked: A villain wants revenge on the hero for putting him in prison so he holds the entire city hostage with bombs, all set to go off unless the hero shows up alone to fight.
Exploited: The chief is actually a Dirty Cop working for the bad guys. He plans to take out their best cop by continually sending him out on dangerous missions alone in hopes of getting rid of him.
Defied: The hero has one or more partners helping him.
Discussed: Citizens in the city wonder why the other cops can never solve the problems and they have to rely on one guy all the time.
Conversed: "This movie is awful! They're in New York! There should be a more than one cop in that city!"
Implied: The hero fights the bad guys and someone asks why he's alone. The answers, "Trust me. He's all we need."
Deconstructed: The hero goes in alone and ends up making a mess since he can't take care of the situation by himself.
Reconstructed: As it turns out, it was all just a Batman Gambit. He made himself look as if he failed so that the Big Bad would get overconfident and make a series of mistakes, allowing the hero to defeat him.
Played For Laughs: A crimewave hits the city with an army of criminals rampaging through the streets. A brave, young officer rushes into his precinct, expecting his fellow officers to be gearing up for the oncoming battle. Instead, he finds an empty building with a single note on the door reading, "Sorry, you're on your own."
Played For Drama: A cop barely survives a terrifying attack on the precinct, resulting in all the other officers getting killed. He tries to do the best he can in a traumatic situation.