One collapse that people often point to is the 1969 Cubs (year of the Miracle Mets). Only ranks 13th on the link you provided. However, the crazy thing about that year was that the Cubs had a 7.5 game lead with 41 games to play and not only did they not make the playoffs, they finished 8 games in back of the Mets. So, they actually could have had a 15 game lead at that point and they still would have missed the playoffs. That’s why when I think about potential swings I also consider swings like that one, and ones experienced this August by the Red Sox, Mets, and Padres. Losing 11 games in the standings in the last 23 games, which is what the Brewers would have to do now to avoid winning the division, is extremely unusual, if not completely unprecedented, for a team that is in playoff contention in September. But, falling 7 games or more in the standings with 45-60 games remaining is much less uncommon. The 1995 Angels, who head this list, had an 8.5 game lead with 33 games left. But they lost the division not to the Rangers, who were in second place, but to the Mariners who were 13 games back on August 2 and still 11.5 games back on August 25. I did a little more digging on the 69 Cubs team. They were up by 4.5 games with 24 games to play (Sept. 5th, 1969) and then finished 8 games out. So, they could have had a 12 game lead at that point and still missed the playoffs. They went 6-16 from Sept 6th to the end of the season, Met's went 22-5.