And it's a local sound, it's based out of Los Angeles, the key figure is this here DJ Mustard (who produced "Rack City")
Andrew Nosnitsky mentions it in this Pitchfork overview of the year in hip hop:
"The rigid clap driven wave of West Coast ratchet music quietly ruled the year. While Tyga's DJ Mustard-laced "Rack City" might have represented the commercial peak of the sound, elements thereof continued to be absorbed by radio playlists via the likes of Rihanna's "Birthday Cake" and Drake's "The Motto" all year long. The energy was a welcome reprise to the usual moping that Drizzy brings to the airwaves. Meanwhile the scene's Californian representatives-- YG, Problem, Iamsu, Loverance and pioneer/permanent fixture E-40 (who released about a hundred songs across five albums this year)-- continued to stitch the threads of hyphy and jerk music into a more contemporary quilt to much commotion in the homeland. They're not just gaining momentum in Los Angeles and the Bay Area either, but in the less charted locales between like Bakersfield and Fresno, inspiring above the head hand claps and below the waist cheek claps."
More stuff on Ratchet and Mustard here and here and here