Lin, for those just hearing of him for the first time, is a Taiwanese shortstop.
The Red Sox signed him for $2m, the largest bonus ever given to a Taiwanese position player, when he was eighteen. The Yankees had attempted to sign him two years earlier, but there was a Tazawa-style incident about big league teams poaching high school students, and the deal fell through. The Sox swooped after he graduated.
Until this season, he's been a glove-first shortstop, although some scouts question if he has the arm for an everyday SS in MLB. He had risen quickly through the system because of his defensive maturity, but stalled out at AA because he couldn't break a .600 OPS against Eastern League pitching.
But this year, he tweaked his swing to get a higher launch angle and suddenly started destroying the Eastern League. He's still only 23.