Strength and agility, but also endurance and speed.
Drills for improving your pitching mechanics, giving you realtime feedback and reference points. But also drills for the mental aspect of pitching, such as concentration and handling disappointment and frustration.
Drills for improving your catching mechanics and for knowing what to expect from a pitcher when asking for a certain pitch in order to be able to help the pitcher if needed.
Drills that cover the basic technique of fielding, but also awareness of what is happening on the field.
Recognizing the various pitches and locations and improve your hitting technique and timing.