Student or Learner
After originally being selected as a ODI pinch hitter as Sri Lanka developed new ways of scoring quickly, Jayasuriya adapted quickly and became a prolific Test scorer, eventually topping the country's record tables for both forms of the game.
I know prolific means (in a large amount) but this doesn't fit in above sentence.
So, please explain the higlighted group of words.
pinch hitter = In cricket, pinch hitter is the usual term for a batsman promoted up the batting order in order to score quick runs.
prolific Test scorer = makes lots and lots of runs in Test matches.