"I've never seen you at a practice. I'm sure you're plugging away at the office. But I'm out here, on the field, trying my best to teach these children how to play a sport they love, while my bank account suffers."
He explains how much easier it'd be to just stay on the sidelines instead of putting himself in a position to be criticised.
"I'm part of this community too and it's no picnic being out here on this stage like this. It's a lot easier back there with the other parents where no one is second-guessing you."
The coach goes on to remind parents that, after the game finishes and they all go home, he still has a lot of work left to do before he can join his family back home for a meal.
"After this game is over, I'll be the last one to leave. I have to break down the field, put away all the equipment and make sure everyone has had a parent arrive to pick them up. There have been evenings when my son and I waited with a player until after dark before someone came to get them. Many nights I'm sure you've already had dinner and are relaxing on the couch by the time I finally kick the mud off my shoes and climb into my car, which hasn't been washed or vacuumed for weeks."
He reminds parents that it'd be nice sometimes to be asked if he needs a hand with anything.
"Do you know how nice it would be if, just once, after a game one of you offered to carry the heavy gear bag to my car or help straighten up the field?"
"If I sound angry, I'm not. I do this because I love it and I love being around the kids. There are plenty of rewards and I remind myself that while you're at the office working, your kid is saying something that makes us all laugh or brings a tear to my eye. The positives outweigh the negatives. I just wish sometime those who don't choose to volunteer their time would leave the coaching to the few of us who do," the letter finishes.
The letter has been shared more than 3000 times on Facebook, many of those in the last few hours.
Social media users sharing the letter hope to remind others of the need to show appreciation for those who volunteer in all manner of fields.