7. Kolten Wong's contract extension (2016)
Kolten Wong was a 25-year-old whippersnapper when he received a five-year contract extension before the 2016 season. In just over two previous seasons, Wong had a .251 average in 1,108 plate appearances. The Cardinals had faith that their 2011 first-round draft pick would continue his upward trajectory, and it worked out for the most part.
Over the next five seasons, Wong had an average of .267, and by the end of his tenure in St. Louis, he had developed into an elite defender at second base, winning Gold Glove Awards in 2019 and 2020. His best season came in 2019, where he hit .285 with a .784 OPS. Despite his success, the Cardinals declined his contract option after the 2020 season, and he became a free agent.
The Milwaukee Brewers signed Wong prior to the 2021 season, and he had a strong first year at the plate, with a career-high 14 home runs and an average of .272. However, his defensive skills eroded significantly, and they continued to decline in his next season with the Brewers and after his trade to the Seattle Mariners in 2022.
The Cardinals' extension of Wong in 2016 resulted in a second baseman who was a solid contributor on offense and defense throughout his time with the team. While Wong's first season with Milwaukee appeared to confirm many Cardinals fans' fears that letting him walk in free agency was a mistake, he has not had the same success since, and it looks as though the Cardinals made the right decision.