Strikeouts (SO) have generally parallelled SO / Sq. Ft of foul area from 1954 to 2000, with their curves easily distinguishable.   Foul area decreased dramatically by about 14% through the period.  However, as foul area decreased approximately 10% through the 90's alone, the relationship between SO (left y-axis) and  SO/ Sq. ft. foul area (right y-axis)  changed dramatically, with the latter increasing by 22%, the former by 10%.  The curves became virtually superimposed.  Certainly there was a dramatic increase of SO in the 90's, for whatever reason.  Yet that does not alone explain the relationship of SO per square foot.  The curve supports the intuitive concept that a decrease in foul area (which allows more foul balls to go into the stands, fewer to be caught on the field, allowing for more SO on subsequent pitches)  contributes to an increase in SO.  It is likely not  the only factor, or perhaps not the primary factor, but the dramatic change in the relationship parallelling a dramatic change in foul area is eye-catching!  Other high-SO periods ('64-68), demonstrated a wider separation of the 2 curves, where average  foul area was greater.