NFL : Biggest year to year declines 

                                           Change in
    All Time:                               win %
  1 Tennessee Titans       1993 -> 1994    -0.625   (0.750 -> 0.125)
  1 Houston Texans         2012 -> 2013    -0.625   (0.750 -> 0.125)
  3 Chicago Bears          2001 -> 2002    -0.563   (0.813 -> 0.250)
  3 Carolina Panthers      2015 -> 2016    -0.563   (0.938 -> 0.375)
  5 Atlanta Falcons        2012 -> 2013    -0.562   (0.812 -> 0.250)
  5 Atlanta Falcons        1998 -> 1999    -0.562   (0.875 -> 0.313)
  7 San Francisco 49ers    1998 -> 1999    -0.500   (0.750 -> 0.250)
  7 New York Giants        2016 -> 2017    -0.500   (0.688 -> 0.188)
  7 New England Patriots   1980 -> 1981    -0.500   (0.625 -> 0.125)
  7 Indianapolis Colts     2010 -> 2011    -0.500   (0.625 -> 0.125)
  7 Denver Broncos         1998 -> 1999    -0.500   (0.875 -> 0.375)
  7 Dallas Cowboys         2014 -> 2015    -0.500   (0.750 -> 0.250)
  7 Baltimore Ravens       2006 -> 2007    -0.500   (0.813 -> 0.313)
 14 San Francisco 49ers    1981 -> 1982    -0.479   (0.812 -> 0.333)
 15 New York Giants        1986 -> 1987    -0.475   (0.875 -> 0.400)
 16 Tampa Bay Buccaneers   2005 -> 2006    -0.438   (0.688 -> 0.250)
 16 Philadelphia Eagles    2004 -> 2005    -0.438   (0.813 -> 0.375)
 16 Oakland Raiders        2002 -> 2003    -0.438   (0.688 -> 0.250)
 16 New Orleans Saints     1979 -> 1980    -0.438   (0.500 -> 0.062)
 16 Los Angeles Chargers   1999 -> 2000    -0.438   (0.500 -> 0.062)
 16 Green Bay Packers      2007 -> 2008    -0.438   (0.813 -> 0.375)
 16 Detroit Lions          2007 -> 2008    -0.438   (0.438 -> 0.000)
 16 Detroit Lions          2000 -> 2001    -0.438   (0.563 -> 0.125)
 16 Detroit Lions          1991 -> 1992    -0.438   (0.750 -> 0.312)
 25 Washington Redskins    2012 -> 2013    -0.437   (0.625 -> 0.188)
 25 Tennessee Titans       2003 -> 2004    -0.437   (0.750 -> 0.313)
 25 Los Angeles Rams       2001 -> 2002    -0.437   (0.875 -> 0.438)
 25 Jacksonville Jaguars   1999 -> 2000    -0.437   (0.875 -> 0.438)

    Last season:
    Jacksonville Jaguars   2017 -> 2018    -0.312   (0.625 -> 0.313)
    Arizona Cardinals      2017 -> 2018    -0.312   (0.500 -> 0.188)
    Minnesota Vikings      2017 -> 2018    -0.282   (0.813 -> 0.531)
    Philadelphia Eagles    2017 -> 2018    -0.250   (0.813 -> 0.563)
    Carolina Panthers      2017 -> 2018    -0.250   (0.688 -> 0.438)
    Pittsburgh Steelers    2017 -> 2018    -0.219   (0.813 -> 0.594)
    Detroit Lions          2017 -> 2018    -0.188   (0.563 -> 0.375)
    Buffalo Bills          2017 -> 2018    -0.188   (0.563 -> 0.375)
    Atlanta Falcons        2017 -> 2018    -0.187   (0.625 -> 0.438)
    San Francisco 49ers    2017 -> 2018    -0.125   (0.375 -> 0.250)
    Oakland Raiders        2017 -> 2018    -0.125   (0.375 -> 0.250)
    New England Patriots   2017 -> 2018    -0.125   (0.813 -> 0.688)
    New York Jets          2017 -> 2018    -0.063   (0.313 -> 0.250)
    Cincinnati Bengals     2017 -> 2018    -0.063   (0.438 -> 0.375)
    Green Bay Packers      2017 -> 2018    -0.032   (0.438 -> 0.406)