Please correct me if I'm mistaken, but according to my calculations, there are 177 days in the ML season. A guy has to accrue 172 days of ML service time to be given a year of playing time. So, let's say you call him up for 20 games as a September call-up. If you hold him down the following season for 24 minor league days, then he would only play 151 days in the ML that season (since the minor league season starts 2 days after the ML season). So his total ML service clock time at the end of that season would be 171 days and he would get an extra year of arb. Check out the FAQ's for more info. (Under the Admin Office tab --> Help --> FAQ --> Players).