All data from Baseball Reference and the BR Play Index.
Kershaw's Game Score in NLCS game 6 was 39. Hendricks had 80, tied for his 2nd best this year, including the post season (best was 81). His average GS in the regular season was 61.2. Kershaw averaged 70.3.
Kershaw's 39 was his lowest of the season, including the post season (he had a 40 on June 26).
So Kershaw was 31 below his season average and Hendricks was 19 above his. That is a swing of 50.
Kershaw's Game Score in NLCS game 2 78 game 6 39 (11th best of 14 post seasons starts), Avg of previous 13 was 55.15
I looked at the "swings" from all world series and LCS final games since 1912.
the ALCS in 2012 with the Scherzer-Sabathia, the swing was 53.5. Their
respective averages and final GS were 55.6-69 & 58.1-18
only other time there was a bigger swing than Kershaw-Hendricks this
year was in the 2013 NLCS with the Kershaw-Wacha matchup. Their
respective averages and final GS were 66.9-17 & 57.44-77. So that
was a swing of 69.46.
The next highest was a 29.84. So interesting that Kershaw was on the wrong end of two of the worst since 2012.