"1-Adam-12, 1-Adam-12, please respond to a 10-101 ... sighting of tropes seen in this episode":
Berserk Button: Not helping matters after Malloy and Reed are shot at, and the revelation of Officer Allen's shortcoming – his stutter – that really has his training officer, Officer Woods, wanting to skin his hide. Reed and Malloy, who had every reason to be even angrier, avert this trope, simply wanting answers; in fact, Malloy tells the usually-reserved Woods to cool it before he begins going over what happened with Allen.
By-the-Book Cop: While handling a landlord-tenant dispute, Allen recites from memory the California Penal Code for breaking and entering to the tenant. Reed lets him finish, then pulls him aside and talks to him about how what he did could have caused more problems.
Eager Rookie: All Donald Allen wanted to be in life was a police officer, and indeed he has the potential to be one of Los Angeles' finest. The only thing standing in his way is something he can't control: his stutter. Otherwise, he makes typical rookie mistakes, just like Reed and Malloy before him in their rookie days.
Pressure Point: The trope is Exactly What It Says on the Tin for Officer Donald Allen, a rookie officer where something about him will reveal whether he has what it takes to handle high-pressure situations, such as warning Malloy and Reed they're about to be shot at by two armed robbers with nothing to lose. Don't worry: The two officers sense what might be about to happen and use their instincts to duck for cover when shot at.
Speech Impediment: It is Officer Allen's stutter, which manifests itself in high-pressure situations, that can have dangerous if not deadly consequences for officers Malloy and Reed. In the end, Allen is forced to admit his handicap and voluntarily resigns.
