• Throwing arm wrapping around their head
• No turning of the body; they throw with their shoulders squared up to the target the whole time
• Elbow dropping to the rib cage (typically called "throwing like a girl" although I've seen boys do it too)
• Striding off-line
• Glove arm hanging down at the side like it's broken
• Glove arm swinging out to the side (swimming)
• No use of the legs — all arm throw
• Arm weakly making a throwing motion causing the ball to float or arc
• Catching with one hand while the throwing hand hangs down limp
• Throwing hand plastered to the webbing of the glove as if the glove is too hard to close with one hand

That's just a sampling. There are more, too, but space prohibits me listing everything.

All of the above are likely to create errors — errors that can cost you runs, and even games. There's no need for that to happen.

Instead of letting your players warm up by chucking balls to a partner any which way while they talk to each other (and you talk to the parents or other coaches), make that time about quality catch. Spend hours if you have to in order to make the point, but give your players instruction and teach them the proper way to throw and catch. Based on what I've seen recently, it will be a huge advantage for your team, and one that doesn't require any special talent to accomplish.

Remember, the fewer runs you allow, the fewer runs you have to score to win. It all starts with quality throwing and catching skills.