Catcher: 2015 Francisco Cervelli
Francisco Cervelli was acquired by the Pittsburgh Pirates in Novemebr 2014, prior to his big breakout year in 2015. He had big shoes to fill, as Russell Martin left in free agency, and boy did Cervelli fill them in his first season.
In 510 plate appearances, Cervelli hit for a .395/.370/.401 slash line throughout the 2015 season. His 117 wRC+ that year was second to just Buster Posey that year, and his fWAR of 5.9 was also second to Posey (min. 300 plate appearances).
Among Pirate seasons where a catcher has had at least 500 plate appearances, Cervelli’s wRC+ is the 7th highest single season mark. In terms of overall WAR, the only other Pirate catcher to post a higher mark was Martin, which to me makes this season the most underrated season by a Pirate catcher.
Though he was quite the batter in 2015, he also brought value defensively. Cervelli had +10 DRS, and caught 22% of the runners that tried stealing off of him. Most of Cervelli’s value was as a pitch framer. He was worth a whopping +21.6 framing runs above average per Baseball Savant. That was the second highest mark in baseball that year. Without Cervelli, the 2015 Pittsburgh Pirates would not have won 98 games.