Excellent explanation. Those Turks, they know how to liberate Constantinople.
Denominator is right. The formula is:
hits+bb+hbp
-----------
AB+bb+hbp+sf
AB excludes sf and sac bunts, but only sf is added back in. Saying that a sac bunt is a fielder's choice is right, kinda, but it's not exactly helpful since it's excluded from AB. If you're gonna penalize the batter for sf, why not sac bunts?
I don't know, this has already received way more attention than it deserves.