Off season is a time for building your endurance and stamina. Make sure fielding drills focus on duration and intensity. Repetition of movement is part of it. make sure the drills are timed with their rest to develop the anaerobic system

http://www.softballperformance.com/softball-drills/softball-conditioning-drills-to-work-on-stamina/

One of my favorite is called pick -ups. You will need a partner for this one. Set up cones about ten yards apart. While you start in the middle of the cones have your parner roll a ball to one cone while you shuffle to pick it up. As you catch the ball bare handed and toss it back they roll another ball to the other cone. Go back a forth about 25 times then break. Focus on your footwork and tracking the ball into your hand. time yourself and try to beat your time each turn

Ok well im onley a player but i think that coaches should have my opion to.But my faveorate drill and the drill that is the most sucessfull drills i think that we do are sucusides wich is going to 1/4 of the gym, going to 1/2 court, 3/4 court, and then all the way and back then you start again after a break and go back wards and then we do lunges down and back and forth even though my thyes burn while doing them it makes my thyes and even but stronger and they need to go slow and take there time.