Other mistake: When the deaf woman is delivering a baby, the subtitles read that Johnny is saying, "The head is rotating," when in fact it's Roy saying that. Subtitles from Universal Studios 2010 DVD.
Other mistake: When Station 51 is at the scene with the electrocuted man, he's dangling from a rope below the second stem of the letter H, in the large sign which reads "HOTEL", above the striped awning. In the shots from above the sign, looking directly down as they set up the ladder, we can see the letter H and the awning, but the dangling man is simply not there in the shots from this perspective, even though we should be able to see him.
Other mistake: When Engine 51 pulls up to the hotel with the injured man dangling from the hotel sign, Captain Stanley addresses Chet and says, "Chet, Roy and John'll need a line," but the subtitles read, "See that? Roy and Dan'll need a line, " even though there isn't anyone named Dan. Subtitles from Universal Studios 2010 DVD.
Other mistake: When the tones drop and Station 51 is dispatched to a "man injured", there is a closeup of the guys running from the kitchen into the apparatus bay, heading for the squad and engine, and none of them are actually 51's guys.
Other mistake: During the fire at the chemical plant, when Captain Stanley and Roy find the missing man and carry him out, the subtitles read that Johnny says "All right, grab his feet," when in fact it's Captain Stanley who says that - Johnny's not even in the same room with them. Subtitles from Universal Studios 2010 DVD.
Other mistake: When Johnny brings the officer who was shot into the ER, as soon as he's loaded onto the gurney Carol takes his BP then tells Brackett his BP, but she also tells him that his pulse is 120, even though she never took his pulse. Additionally, when Morton places the blood vials on the tray and tells the nurse, "I want this sent to the lab STAT, type and cross match, and CBC and differentials STAT," due to the urgency of the situation, but the nurse doesn't leave, she just stands for the rest of the scene.
Other mistake: When John, Roy, and Vince grab the officer who was shot by the sniper and make a run for it, as they duck behind the car, right behind them we can see a city bus just driving on by the lot, directly in the sniper's line of fire, even though that area's supposedly closed off with heavy police presence.
Other mistake: When John and Roy treat the 12 year old boy in anaphylactic shock, Early states, "Start IV D5W, 1 milligram epinephrin IV push," and John confirms the order. Then after giving Rampart a new set of vitals which are poor, Early orders, "Add 50 milligrams Benadryl IV push." But when John confirms that order he only says, "1 milligram epinephrine IV push," (which is the earlier order) and Early actually okays John's incorrect repeat of the order, even though John did not confirm the order of "50 milligrams Benadryl."
Other mistake: After Station 51 is dispatched to the 'vehicle accident with injuries', in the exterior shot as the squad and engine roll out, we can see the real Station 127's vehicle is still parked inside the apparatus bay, near the rear bay door.
Other mistake: When Squad 51 is dispatched to the liquor store shooting, en route they are almost hit by a driver who passed a stop sign at the intersection. This is the same footage from season 2, episode 13 "Drivers", when the squad is almost hit by a car while responding to a football injury.
Other mistake: At the scene of the vehicle accident, with a raging fire going on, the Chief communicates over the HT with Copter 10, and when Copter 10 arrives and makes the water drop, it is actually Copter 14 we see in all the shots.
Daisy's Pick Blind Date - S4-E7
Other mistake: When Squad 51 is dispatched to "man needs assistance", in the exterior shot as the squad rolls out of the apparatus bay we can see Engine 51 still inside the bay, but the real Station 127's engine is parked right beside the station house.
Daisy's Pick Blind Date - S4-E7
Other mistake: When dispatched to the fire in the theater, the companies called are Station 51, Engine 85, and Station 36, but at the scene of the fire we see Engine 9 roll up and also see firemen with 19 on their helmets. These are shots from previous episodes including 3x7, "Promotion", when Roy and John rescue the security guard at the structure fire.
Daisy's Pick Blind Date - S4-E7
Other mistake: When Johnny and Roy are in the ice house, there's a closeup of Johnny's arms as he's hosing down the ice and removing it from the hypothermic victim's arm, but it's obvious that the dark hairy arms belong to the stunt double, not to Johnny.
Other mistake: During the rescue at the top of the open drawbridge, in the shots of Engine 2 we can see the red, vinyl material with the company number imprinted on it, adhered to the front of the engine.
Other mistake: When Station 51 is dispatched to 'man trapped in vehicle', we can see the real Station 127's vehicle is still parked inside the apparatus bay, near the rear bay door.
Camera Bug - S4-E10
Other mistake: When Engine 51 and Squad 51 first roll in during the school fire, we see the burning building has a flat roof. After Johnny and Roy have rescued the unconscious boy from the classroom, there is a closeup of two firemen standing on a slanted, tiled roof with a hose, which is from episode 3x2, "The Old Engine", just before 17's Captain Harmell falls through the warehouse roof.
Camera Bug - S4-E10
Other mistake: While Roy and John are at 68's, Roy goes to the stove to see what Bob was cooking when he started having pain, and the closeup footage we see of the pot of bubbling chilli is the same as some of the footage of Chet's chilli in 4x1, "The Screenwriter," when 'Miss October' stops by the station.
Camera Bug - S4-E10
Other mistake: At the end of the episode, when Johnny's telling the other guys that his photograph was bought, the box of cereal and carton of milk that are on the table have tape affixed to them, to deliberately cover their brand names.
Other mistake: During the structure fire, when Engine 98 rolls up we can see the large red vinyl adhered to the top of the engine's cab. Then, when Truck 106 rolls up we see its company number 106 on the door, but in the overhead shot we can see the number 8 on the roof of the cab, not 106. This presumably means that the door has one of the prop dept's magnetic decals imprinted with 106, and the roof still shows the Truck company's real number.
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 ★