I 100% believe (just know) that when Coach saw Stiles with Derek during parent-teacher conferences for Eli he just looks Stiles dead in the eyes like, “Bilinski? What the hell.... Who's parent are you?” before checking the schedule and just going, “yeahhhhh... This checks out.”
This is how I pictured Coach meeting Eli whe he applied for the lacrosse team
Coach: Next, Elias Hale
Eli: Hi-
Coach: I said Hale, go back in line Stilinski
Eli: I-
Coach: Can't you heard Stilinski? I said back in line!
Eli: But I'm not-
Coach: You know what? Alright, your in. If I saw potential in your dad I guess I can work with you.
Eli: Sr. I thi- wait… are you really gonna give me the position?! I haven't even played?
Coach: So?
Eli: …
Eli: Nothing, thanks for the oportunity.
Later that day:
Derek: So… how was practice? did you get in?
Eli: Actually, I did.
Derek: Awesome, I'm so excited to go cheer you up.
Eli: That's great dad, but just remember: You must sit besides the Sheriff and follow the player with the Stilinski lastname.
Derek: …
Eli: …
*Stiles astral proyecting himself since cuantico to the living room*: WhY diD I Just ReceIVed a mAil fROM Coach to CheCk thAT "My SoN" Can PLAy in THE NExt game?
Eli *running up the stairs*: Maybe I should go to my room to do my homework. Please Stiles, I need the form signed for thursday. I love ya, bye.
Stiles: Did he just-
Derek: Idk, it's your kid.
Stiles: But-
Derek: ALL YOURS.
Stiles: I hope you fuckers have an explanation as to why I was not told that my family was being suicidal by trying to kill the very demon that had possessed me years ago!