My grades were going well from the start but on my final year of hs my grades dropped because of the game practices and matches i played for my hs and now i am confused what to do ! My friends told me to ask the coach to write a letter to the admission officer describing him the reason behind my grades drop.
I want to know is it a good idea ? If not then what should i do ?
You chose to prioritize those practice and matches over your grades. That was your choice.
Don’t ask the coach to write a letter. What could he possibly say that would explain why your grades dropped but thousands of other fall athletes have managed to maintain theirs?
Instead, now, on Sunday morning, do everything you can to pull those grades up. What quizzes are coming up this week? What tests? What reading do you have to do?
Do everything within your power to pull up your grades for this marking period. What matters on the transcript is the grade at the end of the marking period, not the October 4 grade.
listen to bjkmom, not your friends. College adcoms want to know that you can manage your workload and other activities. The term isn’t over: knock yourself out getting your marks up. If there is still a visible drop, consider writing one of you essays on learning the lesson of time management 
This says you prioritize play over work. Do not draw more attention to negatives. Your application package is an opportunity to display yourself in a positive light and leave a good impression. Do not make the focus of your application an apology and leave a impression that you’re always going to make excuses.