An elbow jabbed Naomi Williams squarely in the ribs as she pushed her way into line alongside the other inmates. Though yard time was almost always uneventful, today some idiot newcomer had thought it would be a good idea to heckle her while she ran sprints up and down the fence.
I'm generally not fond of using the protagonist's full name in anywhere except in dialog. It drags me out of the narrative before you've had a chance to pull me in. Especially not in that crucial first paragraph. Is it important that we know her full name right off? I'm not really grabbed by this. I *want* to be - an inmate as protagonist is interesting, but I'm not quite getting it. Maybe have Naomi reacting to getting jabbed by an elbow, or getting knocked to the ground. Something to show us that something exciting is going to happen. It's reading a little flat as-is
The other girl smirked at her now, gunning for a fight. Naomi looked away just long enough to roll her eyes. It was only a matter of time before the newbie learned she shouldn’t mess with the only convicted murderer in the facility. Normally Naomi would’ve delayed that particular lesson, but hearing catcalls while exercising in eighty-five degree heat hadn’t exactly improved her mood.
I think you could bring the first and second paragraphs together and make it more punchy to really draw your reader in.
As they marched inside in a straight line, she kept her eyes on newbie’s back. Right before they passed the guards Naomi stepped hard on her heel, sending her stumbling into the girl in front of her.
The guards were on newbie’s case right away, thinking she’d tried to start something. When she protested that she’d been tripped, they only bothered her more. Meanwhile, Naomi kept her face blank and her eyes facing forward. Three years in lockup and she knew exactly how to stay out of trouble—and how to cause a little if necessary without getting caught. All she wanted was to be left alone, and putting the occasional person in their place was a small price to pay for solitude.
By the time they finally shoved the newbie back into line, Naomi almost felt sorry for her. Almost.
This leaves me wondering why you chose to start your novel here? Is the newbie somehow going to play into the rest of the story? I get you're trying to draw the reader in with the interesting twist that the MC is an inmate convicted of murder. I just wonder if this is really where you want to start the book out? I think with combining the first and second paragraphs and making it more succinct would really help strengthen this opening.