Complex sentence: Additionally, contrary to popular belief, performance actually decreased the year after the contract year instead of going back to the baseline: in the NBA, PER went up during the contract year, but below baseline the year after signing said deal.
Split into simpler sentences: Additionally, contrary to popular belief, performance actually decreased the year after the contract year instead of going back to the baseline. In the NBA, for example, PER went up during the contract year, but below baseline the year after signing said deal.