Why does a shot put have to be thrown differently than a tennis ball/baseball? I never understood why a shotput in track and field has to be thrown in that squatting and pushing kind of stance whereas with a baseball or tennis ball, you just try to throw it as hard as possible, usually by swinging your arms. In both cases, you get a farther distance using those ways but if you throw a tennis ball like a shotput or vice versa, it does not work at all.
Practically, it makes sense to throw those things in their own special way but science-wise they are just balls with a mass. Is it because the tennis ball is hollow? But then in that case, a baseball is not hollow just like the shotput, but it has to be throw in the tennis ball way.
 A: A shot (for men) weighs 16 pounds. A tennis ball weighs 2 ounces. A shot has the same mass of 128 tennis balls.
Try throwing a bag containing 128 tennis balls using just your arm, and you will see why that isn't very effective.
The limiting factor in throwing a tennis ball (or a cricket ball or baseball) is the speed your hand is moving when it releases the ball.
The limiting factor in putting a shot is the amount of work you can do to accelerate the shot before you release it. To get the maximum acceleration, you need to use all the muscle groups in your body, not just your arms. That is why you start from a position where you can apply a force to the shot using your legs, where the muscles are more powerful than in your arms.
In fact, to throw a tennis ball a really long distance you also use your leg muscles, because you  are running forward when you release the ball and your legs are accelerating your whole body in the direction of the throw.
Incidentally, the laws of cricket say that the bowler much keep his/her arm straight when delivering the ball, which actually reduces the maximum speed that can be achieved - though many "fast bowlers" can release the ball at speeds from 90 to 100 mph or 40 to 45 m/s. Baseball pitchers can reach similar speeds, with a heavier ball but no restriction on "straight arm" throwing. The typical release speed for a shot in athletics competitions is 10 to 12 m/s.
The world record distances for throwing a tennis ball, cricket ball, or baseball are all similar at about 130m, compared with 23m for a shot.
A very simple model of projectile motion gives the correct order of magnitude for the world record throws. Suppose the ball is thrown with speed $v$ and released at ground level (i.e. ignore the height of the thrower). Ignoring air resistance, the optimum angle to throw the ball is $45^\circ$ to the horizontal. From the SUVAT equations we get the horizontal distance thrown = $v^2/g$. Taking $g = 10$ m/s that formula gives a distance of $14.4$ m for a shot released at $12$ m/s, and $160$ m for a tennis ball released at $40$ m/s.
A: There's a rule in shot put that prevents you from swinging the metal ball, which states that "at any time if the shot loses contact with the neck then it is technically an illegal put" (from https://en.wikipedia.org/wiki/Shot_put).  Therefore, the best way to launch the metal ball is to swat down and push, respectively because you can make use of the normal force from the ground and the only available motion you can use to accelerate the ball from your neck is by pushing.
