Even if you didn’t remember the exact point at which Yu Darvish started throwing a knuckle-curve last season, you could spot it easily by looking at game logs. If you pull up FanGraphs, you’ll note that his curveball percentage spiked to 16.9% on August 21 in a home start against the Giants. Baseball Savant will show you the same thing, along with a whiff percentage that jumped to around 45% after having been almost nil in 25 previous starts.
Yu Darvish added a knuckle-curve to his repertoire late last season.