Arm: This is a players throwing arm.. the better the rating the faster the throw in fielding and fast ball pitching.
Bat: This is the players batting average or the ability to make a hit to allow runs or make it to base or batting control to hit the direction you'd like
Defence: This is their fielding ability to catch pop flies or stop ground balls or prevent making errors.. If your wondering what errors look like try putting mikey as a short stop and trying to stop a ground ball rolling towards him. If he doesn't stop it he makes a weird look and pauses and you have to run to the ball again to grab it.
Speed: This is a players running speed both on the field and base running.
Power: This is the ability to hit home runs and make the ball pop up in the air and get height. The more power the farther the hit.
Stanima: This is how long and consistant a player can pitch without losing control which you once had. For example Rocky will slow down in speed for his fastball after 3 innings usually where as Josh can keep throwing curve balls till the game is over.
Tricky pitch: This is the control you have over your pitches to throw curve balls or lobs in softball. When you see someone has a good tricky pitch rating, chances are they can throw a really wide curve ball.
I have yet to go through every player as a pitcher and rate them in stanima and tricky pitch. I have however listed what types of pitches each player throws in fastball mode and if they are ok or bad. Meaning if they are ok they are average, poor or bad means don't even bother and great or good meaning good control and you should use them.
Starters and releif players: Again this should be taken into consideration how long a pitcher will last or if a batter hits better at night or on certain fields or if the pinch runner is fast, can avoid tags, or tackle. Once you use a releif player in fastball mode you can not change them till the next game.
You can however mix and match up your field roster so you have access to alot of pitchers.