Visible crew/equipment: After they finally get an address for the attempted suicide Squad 51 takes off, and when Engine 51 pulls away from the curb, the shadow of cinematographic equipment is visible on the engine's front, and the reflection of lighting equipment is visible on the side of the engine.
Other mistake: When they're trying to identify the address of the attempted suicide, Engine 51 stops and is standing by at 223 Street and Ridgely, while the squad drives elsewhere, and when Squad 51 stops it's standing by at 218 Street and Carson. However, when they're dispatched we see that the rigs are actually pulling away from the same corner but facing opposite directions, note the area and background. Then when Johnny and Roy put on their turnouts, in the next shot of Engine 51 it's now driving towards the camera in the opposite direction on the same street they had pulled away from.
Other mistake: When Dixie's on the phone with the suicide attempt, Dixie tells her the date of her own birthday, hoping to get the caller's birthday in return. Then when the caller tells Dixie that the month of her birth is February, while Brackett's listening, they don't contact Early who's with the senior data analyst with that crucial information to help narrow down her identity faster, which was the whole point of Dixie trying to get that information from her.
Other mistake: During the fire at the horse ranch, when Engine 40 rolls up we can see that the engine company's number is covered atop the cab, and the large, red rectangular vinyl material that's adhered to the back of the engine with nothing on it. Presumably covering the real engine company's number.
Other mistake: When the dispatcher sends Squad 51 to the heart attack at the bank robbery location, the address is given as "2057 North Hillcrest, cross street Barker," but when they arrive at the corner bank, the sign reads Celis Street.
Continuity mistake: After John spots a cute nurse talking to Dixie, when he zeros in on Dix for the nurse's name Dixie's holding a pad in her left hand, but in the next closeup her left hand's empty as she gives John an entire run-down on that nurse.
Audio problem: After Johnny gets out of the elevator, Johnny sees a crowd around the treatment room, so Roy tells him that they're interviewing the bank guard who was shot, and when we hear Roy ask, "How'd you make out with the girl from orthopedics," his mouth is saying something different.
Answer: I was rewatching a few first season episodes of Charlie's Angels (1976), and in S1xE6 "The Killing Kind," I recognized the same actor. So, to finally fully answer your question, the two baseball players in School Days are played by Rod Perry and Sean Fallon Walsh.
Super Grover ★