I have no problem with a kid throwing from side arm, or submarine arm slots. Many "experts" are concerned with velocity blah blah. And I think that's great but many kids go thru HS and will never be able to break 84-86 no matter what they, their parents, or their coaches try (mechanics, long toss, work outs, weighted balls, or whatever fancy item or new wave book or DVD they will be happy to sell you). Sometimes it just comes down to genes. It's sad but true.
I feel sidearm/sub can make a average HS pitcher into a very effective member of your staff. I currently have 2 guys...1 sidearm and 1 submarine. Both of these young men would not have been able to pitch at the varsity level throwing "over the top"....... from a velocity and a stuff standpoint. We sat them down and offered them an opportunity to learn a new slot to help out our staff, both agreed because they knew they needed to make an adjustment if they wanted more time on the hill. This year both have ERA's in the ones and do and excellent job both starting and out of the pen. They have both become valued members of our staffs. One young man has even begun to be recruited because of his improvement and new arm slot (he added 2-4 mph to his fastball by just dropping down........go figure) The last young man we had prior to these two went from 5th best pitcher on the team the summer before his senior year to a scholarship player by end of his HS career. None of the side arm pitchers I have coached have ever had arm problems (we teach them the proper way to do it).
With all that said. It isn't for every kid and it isn't for every player. We look for young men who fit a mold to be able to drop down. ANd it is usually our last effort to get something out of him before the end of his HS career. It really helps that we have a coach on our staff with experience as a sidearmer......it paid his way thru college. Many people will turn their nose to the thought of it but it takes coaches willing to think outside the box pitching box sometimes. The downside of dropping a kid down is the fact he will struggle throwing in the field. Once you make that muscle memory it is hard to break and throws from the field (OF and SS/3B) will tend to run and sail. One part of our mold is pitcher only or a 1B man because of the problems they will have defensively throwing. So this might be something you think about before you drop down a 9 year old. But for a college aged player or a HS kid it isn't always a bad idea like the "experts" say. I've seen many a team get beat by those type of kids and in the end isn't that part of our job.....to win a game or two. I'm sure somebody will disagree with me but I'm just a coach.......not an "expert".