There is a decline and there is a drop off.
The 1885 Boston Beaneaters (now the Atlanta Braves) saw a huge drop off under Manager John Morrill during his 4th season. The prior season the ended in second. In 1885 they ended in fifth with a 46-66 record.
In fact, a drop off is being kind. They fell off a cliff. The team’s .411 winning percentage was the worst in its histoy up to that point. That was a 27 ½ game slide from the previous year. And …. AMAZINGLY enough, 41 games behind.