During baseball season, batting practice and fielding ground balls may take precedence during practice, but you still need to make time for speed and agility work. (See 3 Speed and Agility Drills to Improve Your Baseball Performance.) Therefore, you should have these five items on your wish list for agility training equipment.
There is not a coach anywhere who wouldn't want his players to improve their quickness and agility, and the agility ladder, (a.k.a. the speed ladder) is a great tool for enhancing foot speed in a short amount of time and space. (Check out Improve Your Agility With 4 Speed Ladder Drills.)
The hips are one of the most neglected areas of the body to train but one of the most important for a baseball player, because baseball requires rotational movement. Placing a lateral resistor or thera-band around your ankles during drills is an effective way to strengthen your hips. (See also Help Prevent Injuries With Mini-Band Exercises.)
Speed hurdles are similar agility ladders from a speed and quickness standpoint, but because the hurdles have the dimension of height (they usually stand about 12 inches high), they add a plyometric element to your training that would otherwise be missing. (See Develop "Usable Speed" for Baseball With the Florida Gators.)
The reaction ball is great for keeping infielders on their toes. Rolling this multi-sided ball to your infielders tests both their hand quickness and their agility. This training aid can be used for all positions in many different sports. A good and inexpensive alternative is to cut or tear the cover partially off an old baseball and use it for infield practice. (See Reaction Training for Quickness.)
It has been well documented that a strong core is critical for baseball players, and a medicine ball is ideal for training the core. Medicine balls have countless uses on the baseball field and in the gym. They are not cheap, but you don't want to skimp on quality. Among my favorite drills for the core are Medicine Ball Slams and Jump Slams, and they require a top- notch ball, since repeated slams may cause a low quality ball to crack.
See my article on How to Construct a Baseball Workout.