A really simple and amazing exercise that can be done at home to strengthen the throwing arm is the band pull apart. Targeting muscles like the trapezius, rotator cuffs, and rear deltoids, the band pull-apart is an exercise that will correct and improve your posture.
To do this exercise, you need to have a resistance band. For starters, you can start with lower resistance, and as you get stronger, you can increase the resistance gradually.
Stand straight and hold the resistance band with both hands at your chest weight. Now pull the resistance band apart, squeezing your shoulder blades. Soon, you’ll be able to see how much tension you can generate by pulling apart the band.