MLB Strikeouts Rising, Walks Not

One of the things I meant to address in my piece on strikeout rate last Thursday (but forgot!) was the fact that strikeouts are up across the board.  There's been a lot of discussion of this year's spike: MLB-average strikeout rate has cleared 20% for the first time (at least as far back as I've looked at it), and is now at 20.5%.  It was 19.9% last season.

This spike is not a new trend, however:

I just went back to 1980, but strikeouts have been consistently on the rise over the last 35 years (at least).  The slope has been particularly steep since 2006, and has increased every year by an average of 0.5%.

Interestingly, walk rate has simultaneously been almost flat.  This comes despite the fact that on-base percentage has become so much more heavily emphasized in the game over that stretch.

The question, of course, is what's causing the surge in strikeout rate.  Are hitters steadily becoming more willing to trade contact for power?  They could also be biasing toward taking more pitches, but if that were true one would expect walk rates to also increase.

Or is it the pitchers who are just becoming better and better, leaving hitters in the dust?  Or a bit of both?

Furthermore, when is this trend going to slow down?  It might not slow, without action by major league baseball.  This was the subject of a recent roundtable discussion on Effectively Wild.  I think there's a legitimate argument that MLB might need to follow Brian Bannister's suggestion and lower the pitching mound.  Otherwise, we're on pace to see strikeouts occur in one out of four plate appearances by the middle of the next decade.  Yikes.