I have never been the coach to say you must pitch everyday. Although, practice makes perfect and repetition is what makes you better than your competition, there is a limit to what daily practice can really do for you. Everyone is different based on skill level, goals, or athletic ability. Here are a few guidelines to how to practice and some warning signs to when its time to take a break.
First of all, parents, if you have to force your child to go out and practice, you might be wasting your time, money and energy. I am a firm believer that people can do anything they want once they make a commitment to it. Forcing, grounding, bribing you child to practice shows your commitment level but not your child's true passion. I always get asked if a child has talent and my honest answer is if she is willing to put the time into it, has a good attitude during practice, and makes you practice with her, then she will be successful.
As already stated, doing more reps than your competitor will give you an advantage. This is true. BUT! Lets say you hurt your arm from pitching too much and you have to sit out 2 weeks... Hard to win when you are not in the game. Baseball has a pitching limit to saves arms and prevent injuries. There is a common myth that softball pitching is a natural motion so girls can pitch all day and do not require a limit. It is not a myth that the motion is less stressful than the baseball pitching motion but there is a limit. The trick is listening to your body to tell you what your limits are, when to keep going and when to rest.
My rule of thumb is no more than 400 full pitches in a week. This does not include warm up or less than full speed pitches such as long toss or any type of drill that is not done for speed. You can do 50 pitches everyday, 100 pitches 4 days a week, or 400 pitches in a tournament. No more than 400 pitches every 7 days. You can fill in the rest of the days and times with snaps, drills, shoulder strengthening exercises, and every pitcher could use a little extra running. Strengthening your rotator cuff may allow you to pitch a little more than 400 pitches in a week but do not go over the limit multiple weeks in a row.
If you are in a rut, have a bad habit, or just do not seem to progress, then you might be approaching your practices all wrong. If you continue to practice unfocused or without goals in mind, then you are just spinning your wheels. Taking time off is not a bad thing. Let's say you are practicing everyday and you are not seeing progress. I would recommend only pitching 1 or 2 days a week but spend 2 or 3 days a week just going back to the basics such as snaps, power line drills, and "dry" pitches that are full motion without a ball.
Having goals set for practice makes your practice more productive. Are you trying to gain speed? Control? Master a new pitch? Or maybe just focus on your mechanics. Have a stated goal at the beginning of practice and keep focus on your goal for your practice time.
I highly recommend playing an off season sport. Especially volleyball! It will get your legs stronger as well as your core muscles. It also keeps your shoulder in shape with less intense pitching motions. Be careful with cross country if you are a pitcher. They utilize two different energy systems and could take away from your explosiveness off the mound. May not be a problem for everyone but the threat is still there. Basketball is also a great choice because of the sprinting involved and will keep you explosive. When you are enjoying your other sport and giving your mind and body a rest, keep pitching at least one day a week to keep from losing any forward momentum you had going into your other sport.
How often should you practice?
Weeks with no games: 1 day of spins and log toss, 3 long days (work all pitches), 1 light day with focus on speed (fastball only)
Weeks with games: 1-2 days of spins and long toss (normally the day before games), 1 long day (not the day after game or day before game), and a medium day with an extend warm up focusing on control and about 30-50 full pitches.
Length of Long Practice:
Go through a warm up and then pitch until you get "wild," indicating fatigue. Remember to push with your legs for about 10-20 pitches and take about a 5 minute break, sitting and drinking water. Then pitch a second round until you get "wild" again, focus on legs for about 10-20 pitches and then be done.
Once you get tired, you will start to lose form and this is where bad mechanics will creep in. You should be between 80-120 in a practice of you are expected to pitch a full 7 inning game. If you are not there yet, add sprints, running (do not exceed more than a mile), or jumping rope at the end of practice to help get you legs in shape.
One extra reminder. If you are trying to increase stamina or endurance, do exercises mentioned above. Do not use pitching drills to increase stamina. It is a quick way to lose mechanics and make you prone to injuries. Do speed drills on days when you are rested and ready to give them 100% to the mechanics of the drills.