I'm pretty sure all scouts/prospect writers use what BA puts in their handbook in describing starters. A 4/5 has command of 2 major league pitches, average velo, consistent breaking ball, and a decent change. A 3 has one plus pitch, two average pitches, average command and makeup. A 2 has 2 plus pitches, average 3rd pitch, command, and makeup. The definition of a 1 is 2 plus pitches, average 3rd pitch, plus plus command, and plus makeup.