I pioneered functional training for racquetball but never realized it!
Back when I was a boy, I grew up on the farm. In the summer we planted crops and baled hay. I remember many days of 100 plus degrees in the top of the barn, stacking bales of hay that weighed 75 pounds plus. (acclimatization, incline press, bench press) Then we milked cows and I carried two pails of milk to the milk house twice a day; mornings and late afternoons (farmer walk-literally!).
Then I went out for football. The Functional training paid off! I was ready to rumble due to the farm work! Today people pay big bucks to flip tractor tires but when I was a kid it was free on the farm! Why do I digress so much? Training for racquetball needs to be functional. A good trainer will help you stabilize your core strength, and equalize your body strength on both sides. They will also help you with shoulder strength and body integrity as well as rotational style training. (I provide some of this for my monthly athletes on my website.)
You do not have to go back to the farm to train, but you can hire a great trainer to train!
ps: In my days at the USOC in Colorado Springs I have actually met coaches in rural communities who send their athletes to the farm to work in the summer for these very reasons!!