Many players have had breakthrough seasons in 2015, but these are the nine breakouts I believe are most sustainable into future seasons. I picked four starting pitchers and five position players.
I mentioned Archer in my 2014 predicted breakouts column, saying he should jump into the top 10 in strikeout rate; I guess I was just a year off, as he's third in the majors in strikeouts as a percentage of batters faced, behind only lefties Chris Sale and Clayton Kershaw. His slider, now often as hard as 91 mph, has become one of the majors' best, although a big part of its effectiveness is his improved fastball command, so he's getting ahead in the count more frequently and staying there as well. For one example, he has gone to 65 2-0 counts so far this year, after doing so 110 times last year. Getting ahead with your fastball so you can finish hitters off with your off-speed stuff is an old formula for pitching success that I doubt will ever change -- because it works -- and it has helped Archer become a top-five pitcher in the American League.