Every Baseball Player knows that fielding ground balls is one of the most difficult aspects of playing Baseball. Sure, it may seem easy for some, but fielding it correctly, error-free, is what we're talking about here. I'm going to give you some advice on how to develop better skills as an infielder.
Depending on your position, your stance is very critical. You should be loose, but you should be ready for anything, including line drives at your head! As the old saying goes: "stay on your toes!" This is why I learned that your calves and quads play a critical role in the sport of Baseball. Learning how to be on your toes, yet in a ready position, can cause most people to get tired after a few innings. So the first thing you should be doing as an infielder is developing better, more stronger, calf and quad muscles. The best way to do this is by using body weight exercises, using good form. Anything from proper squats to toe raises will help.
Depending on your age, you should be doing body weight training during the off season, but doing so during the season (with plenty of recovery time between games) is also helpful. Many players get together for group workouts. If you're already doing workouts with weights, I encourage you to switch it up and try new things every 6-8 weeks!
Toe raises are pretty simple and will help you get a bit quicker, faster and even jump higher if you do them enough over time. But you should also stretch your calves before and after, too. When doing these toe raises, be sure to point your toes inside, outside and straight forward. I usually do them all at once, 10 raises each way, 3 total sets. I also encourage you to do this every 3-4 days with other body weight workouts.
Squats are another great way to build your leg muscles. Use good form and try different types of squats. Here is a video of a proper form squat. Many people bend their knees too much and put too much pressure on their knees, while doing very little for their quadriceps. Be sure to use proper form!
Stretching is critical. While I won't get into the "best" way to stretch, I will say that static stretching is something I've always relied on, even prior to dynamic stretching. Always do things at your own comfort level and try not to over do things.
Another exercise I have always done is squatting down in the ready position, on my toes, and moving from side to side. If you've ever done any shuffle exercises, it's pretty much like that. In fact, it's similar to leading off base, but in an infielder position, as you were moving to field a ball to your right, then field a ball to your left. Follow that up with some running forward and then hopping backwards. This exercise is great for developing your legs as an infielder.
Now that we've discusses our legs and endurance, let's get into the actual fielding tips and tricks. One exercise my father taught me was something he learned from Matt Williams. Williams' old coach had created a little tool to help him field "softer." This tool was actually just a ping pong paddle without handles, with 2 straps (or you can use shoelaces) that will wrap around the hand to keep it there. The point of the tool is to field the ball softly, bringing the ball in with your hand and not just relying on the glove to catch the ball. Using 2 hands is something that even some Professionals have issues with.
The main point of the tool is to develop a better approach to keeping your eyes on the ball, all the way into the glove, but also bringing the ball into the glove, along with your throwing hand (to trap it), then bringing it up towards you at the same time, in one swooping motion. I used this tool for many years and you don't even need someone to hit grounders. So for fathers or mothers out there who might not be able to help their kid as much as they'd like, you can always encourage them to try this drill at home. All they need is a ball and a wall. In fact, you can even use a tennis ball if needed, although a real baseball would be better. The paddle should get quieter and quieter as time goes by. This means that you're doing it correctly! Soft hands are what makes a great infielder.
Nothing beats repetition. Like anything, repetition makes you better. Practice fielding every day, but each rep should be your best. 100%, nothing less. Just doing a bunch of repetitions doesn't actually help unless you're trying your hardest and learning from your mistakes. I hope this helps and please feel free to provide any other useful tips and tricks below!