By Emma Baccellieri Slider-curve hybrids have been around for decades. Corey Kluber won two Cy Youngs with one. Why is this catching on now? View the original article to see embedded media. Welcome to The Opener, where every weekday morning during the regular season you’ll get a fresh, topical story to start your day from one of SI.com’s MLB writers. ST. PETERSBURG, Fla. — Corey Kluber has long said that his breaking ball resists classification. It’s not a curve. It’s not a slider. It’s just his breaking ball—the pitch that helped him win the Cy Young in 2014 and ’17, and that still bedevils h…