Phil Hughes has recently announced that he will no longer be throwing his cutter. He might have abandoned it after two months of the 2012 season, but that was still enough to ensure it to be the worst cutter in baseball. Of the 44 major leaguers who pitched at least 150 innings and threw a cutter, Hughes placed #44 out of 44 with a -10.28 cutter runs above average per 100 pitches in 191.1 innings. That's pretty horrible, especially when the next least valuable cutter, thrown by Felix Doubront in only 161 innings, amounted to a -3.29 cutter runs above average per 100 pitches. Chris Capuano pitched a more comparable 198.1 innings, but still managed a less bad -2.42.
Over the span of two seasons, Hughes threw a -5.14 cutter, which was only better than Jeff Francis' -6.85 and Brandon Morrow's -7.51. Despite pitching just 74.2 innings in 2011, the value of his cutter was only -3.03, although he actually threw the cutter more often, using it 14% of the time instead of only 2.5% in 2012. His cutter hasn't actually provided positive value since 2010, so it's more than necessary for him to scrap the pitch at this point.
Thankfully, he has adopted a slider to replace it. He threw a slider 3.4% of the time in 2012 and actually acquired a substantial amount of value to his pitch selection. His slider was valued at 2.16 slider runs above average per 100 pitches, which made it the fifth-most valuable slider among pitchers with at least 150 innings. That's a gigantic upgrade. Hughes still relies on his fastball, having thrown it 47.6% of the time, the highest rate in 2012 by an almost 3% margin. His fastball hasn't been worth one run above average since 2009, and provided negative value for the first time in 2012, so if Hughes can mix in a pitch that is actually valuable for him, he might be able to become a good pitcher.
Hughes says that he seeks consistency, but the only way he's going to do that is if he actually changes how he pitches. He can't continue to throw fastballs almost all the time. If he's discovered a pitch that works for him, he needs to actually use it instead of staying married to a pitch that's not even that effective. Between 2010 and 2012 his fastball was valued at 0.37 fastball runs above average per 100 pitches. Do you know which pitchers had a worse fastball in that time, but have still managed to be ridiculously successful? Cole Hamels, Zack Greinke, Roy Halladay, CC Sabathia, and a bunch of other guys you would take over Hughes in a heartbeat. Hughes can have a good career without a very good fastball, he just has to let it happen.