In the bottom of the 4th inning of Toronto's 10-8 loss to Seattle, Blue Jays batter Whit Merrifield with a 3-2 count appeared to take ball four from Mariners pitcher Penn Murfee...except he didn't walk and struck out on the very next pitch. It turns out umpires called a balk and HP Umpire Mark Carlson's mechanics proved insufficient for both teams' broadcasts, which were equally confused as to why Merrifield continued his at-bat having received four balls.
Upon review, with Toronto baserunner Vlad Guerrero, Jr on first base, Murfee committed a no-stop balk—he failed to stop while in Set Position before delivering to home plate, as in Official Baseball Rule 6.02(a)(13), which states, "The pitcher delivers the pitch from Set Position without coming to a stop"—and subsequently threw a pitch outside for what Merrifield and the teams alike initially thought was ball four.
Instead, Carlson's crew called a balk, the penalty for which is to award the baserunners one base from their time-of-pitch occupied bases: for Guerrero, that would mean second base (effectively nullifying his stolen base).
But was this the correct call? Although in high school (NFHS), the ball becomes dead immediately upon a balk, it remains live in pro (OBR) and college (NCAA) until the pitch is delivered. Afterward, the umpire may call "Time" and enforce the balk penalty, if applicable.
Official Baseball Rule 6.02(a) Penalty indicates what happens when a balk occurs: "The ball is dead, and each runner shall advance one base without liability to be put out, unless the batter reaches first on a hit, an error, a base on balls, a hit batter, or otherwise, and all other runners advance at least one base, in which case the play proceeds without reference to the balk."
With a 3-2 count, the pitch thrown to Merrifield—ball four—resulted in a base on balls, which in turn forced the only baserunner (R1 Guerrero) to advance...so why didn't the latter part of the penalty apply, wherein play would proceed without reference to the balk? Why did Merrifield return to bat to strikeout on a 3-2 do-over pitch instead of being awarded first (and Guerrero forced to advance to second)?
The only way this works out from a rules enforcement standpoint is if HP Umpire Carlson would have called the pitch a strike if not for the balk. Because a strike here would result in a strikeout (e.g., the batter would not have reached first base anyway), the balk penalty would appropriately be enforced...but only if the pitch was a strike. Thus, the most likely explanation is that Carlson simply missed the pitch.
Video as follows:
