Continuity mistake: When Squad 51 is dispatched to 'man down', as the squad heads out of the apparatus bay, the engine we see parked in the bay is the old Crown from seasons 1 and 2, instead of their current Ward LaFrance.
Revealing mistake: At the house fire, after Roy and Johnny go upstairs to rescue the invalid woman, Captain Stanley and Chet head to the front door, and just before Cap kicks in the front door, we can see that the door isn't actually closed, it's just ajar.
Continuity mistake: When Dixie is having a heart to heart talk with Karen, in the shot facing Dixie she reaches out with her left hand to take the napkin from Karen, but in the closeup it's her right hand that takes the napkin. Additionally, the napkin she takes from Karen is perfectly folded, but it was wrinkled and messy when Karen held it.
Continuity mistake: When Karen first walks into Station 51, her handbag is over her right shoulder, then over her left shoulder and back to her right shoulder again.
Pressure 165 - S5-E7
Other mistake: When Johnny prepares Chef Michel's recipe, he leaves the casserole dish in the oven while Station 51 is dispatched to the structure fire. When he and Roy return, Johnny opens the hot oven door to find it smoking and the dish bubbled over, and even though the oven door is supposedly very hot, Roy places his hand on the inside of that door and actually leans on it like there's absolutely no problem.
Pressure 165 - S5-E7
Continuity mistake: While Johnny and the doctor are in the pressurized chamber with the diver, the guy outside the chamber tells them that they're at 165 and vetting, as he holds the mic up to his mouth with his left hand, but when it cuts to the interior shot, the mic is held up in his right hand.
Pressure 165 - S5-E7
Visible crew/equipment: When Roy and Johnny are with Chef Michel, the outline of the mic transmitter can be seen on the front of Johnny's shirt.
Pressure 165 - S5-E7
Other mistake: When Johnny brings in the bags full of groceries for the dinner he's cooking, and also later when he discovers that the liquid in the pot turned green, there is tape covering the brand names on the packages.
Pressure 165 - S5-E7
Deliberate mistake: When Roy and Johnny are on the Coast Guard helicopter, approaching Catalina Island with the injured diver, there is a closeup shot of them looking out the windows, which is a flipped shot - note the backwards paramedic patch on the right sleeve, instead of being on the left sleeve.
Pressure 165 - S5-E7
Continuity mistake: After Johnny discovers that the white stuff he left cooking on the stove has turned green, Station 51 is dispatched to the structure fire, so everyone rolls on the call. When Johnny and Roy return, and Johnny decides to dump all the food he cooked, a large stock pot has mysteriously and conveniently appeared on the counter, where it did not exist when they left.
Pressure 165 - S5-E7
Continuity mistake: At the decompression chamber on Catalina Island, after John and Roy introduce themselves to Dr. Scott, the doctor removes the stethoscope from around his neck and puts it down, but in his closeup it's still around his neck, then in the wide shot it's gone, only to return in closeup again.
Pressure 165 - S5-E7
Visible crew/equipment: When Station 51 is dispatched to the structure fire at the flour company, while en route there's a closeup of Squad 51, and the reflection of the filming vehicle can be seen in the spotlight.
The Lighter-Than-Air Man - S5-E8
Visible crew/equipment: When all the guys are on site of an overturned tractor trailer, Captain Stanley says "Let's cool off that cab." In the next closeup of Stoker spinning a gear, the reflection of the cameraman (with mustache and hat) holding a handheld camera is visible on the engine's red surface.
The Lighter-Than-Air Man - S5-E8
Continuity mistake: After Gage opens the baby layette wrapping, he and DeSoto exit the kitchen to answer a phone call. When dispatch calls on Engine 51, the rest of the guys start to pile out of the kitchen, but in the next overhead shot the guys are actually exiting the doorway that leads to the locker room, not the kitchen. The interior of Station 51's setup when facing it is, to the right are Captain Stanley's office and the kitchen, and on the opposite side to the left are the sleeping quarters and locker room.
The Lighter-Than-Air Man - S5-E8
Visible crew/equipment: When Crockett leaves Medford's room with the glass that Medford drank from, there's a mirror over the sink, and in the mirror's reflection we can see the camera's moving shadow on the wall, right beside Crockett's reflection.
The Lighter-Than-Air Man - S5-E8
Visible crew/equipment: When Johnny brings in the box and Chet removes the wrapping for the baby layette, note the unfinished set wall past Engine 51 in the apparatus bay, which we can see since the front bay door is open, but when Captain Stanley walks in telling John about the phone call, the front bay door is now closed, then when the tones drop that set wall can be seen once again.
The Lighter-Than-Air Man - S5-E8
Visible crew/equipment: When the trailer that's on fire pulls up to the front of the station, the outline of the mic transmitter is visible on the back of the woman's blouse.
The Lighter-Than-Air Man - S5-E8
Continuity mistake: When Station 51 is dispatched to the truck fire, as Captain Stanley responds to the dispatcher Roy and Johnny get into the squad, but we see Marco, Mike and Chet head back to the kitchen instead of getting on the engine, then we see both the engine and squad responding to the incident.
The Lighter-Than-Air Man - S5-E8
Visible crew/equipment: When Station 51 is on the scene with the overturned truck carrying insecticide, that's causing toxic smoke, Captain Stanley asks dispatch to identify the toxicity of trimelanide, and three shots later a crew member walks onscreen from the left, right behind the overturned truck, then realizes his mistake and backs away.
The Lighter-Than-Air Man - S5-E8
Continuity mistake: At the scene of the overturned truck causing toxic smoke, when Chet talks to the driver and then pops out the windshield, in the wide shots the two windshields are intact and not cracked, but in the closeups facing Chet and the closeups facing the driver there are long cracks in the windshield.
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 ★