"1-Adam-12, 1-Adam-12, please respond to a 10-101 ... sighting of tropes seen in this episode":
Being Personal Isn't Professional: Reed takes the death of the 5-year-old boy – he had been viciously assaulted by Mr. Bates, a serial sex fiend – very personally, so much that he punches a locker door in frustration. He is likely reminded (off-screen) that this is sometimes how police work is, unfair as it is (and that he and other officers have seen (or will see) far worse), but he can't let personal feelings get in the way of doing the job, otherwise it's a quick way of becoming unable to do the job at all.
In the end, Reed takes this lesson to heart and acquits himself well when, late in the episode, he is repeatedly called a pig and a thug by two Black men (after taking them into custody) who mercilessly gunned down a grocer and his wife – also Black, as it will later be revealed – during an armed robbery. Except to remind the two of their rights, Reed resists the temptation to tell the two robbers and murderers what he thinks of them as he and Malloy are taking them to their police car ... knowing a large group of Black people, just waiting to start a riot, are following them.
Blatant Lies: The opening act, where a man that Reed had just arrested (for lewd acts with a child) smugly boasts he has never seen the booking area of a police station before. Reed reminds the man, Mr. Bates, that he is lying: He has a long criminal history of sex-related offenses – enough to fill a file 2 inches thick – and that his latest crime was his most serious yet.
Broken Tears: Reed has these when he learns the little boy who had been raped had died on the operating table.
Eager Rookie: There are still signs of this in Reed at this point in the series. He still gives his opinion a bit too freely when he expresses his disgust with a sex offender he just arrested (his first such bust), he still lets what happened note – or is implied to have happened; this is perhaps deliberately left to the viewer's imagination, although it is implied to be brutal – to the boy get to him, he wants to begin investigating what he thinks is a dead baby call (actually, it's a bag of smelly fish) and he even forgets to check whether his name badge is correctly aligned.
Smug Snake: Bates, in spades, which really pisses Reed off.
Unlikely Hero: Smith, a teenaged boy who was in the group of Black people that angry that two white officers were arresting two Black men for what they first believe is some petty crime. Smith tells the group that the two men that were being arrested deserved it because they murdered two people – a grocer and his wife – during a robbery they committed, and in essence says they are unworthy of their support. Later, in the locker room, Smith confides in Reed and Malloy that the couple were also Black, and they worked hard to support a low-income neighborhood, often taking losses to help impoverished families, doing everything to support Black teenagers who were looking to go to college, etc. ... and by their murder, it was the two criminals and not the police who wronged the community.
What the Hell, Hero?: What Malloy and Mac try to prevent Reed from becoming, especially after Reed's attitude toward Bates in the holding cell area ... and, it is implied, during the arrest and on the way to the station. note (Ironically, Reed would return the favor years later in "X-Force," when Malloy takes this same attitude toward a Smug Snake who boasts that he was giving a little girl "what she wanted.")
