NF = Nasty Factor

[Déjà Bru]

I'm tracking the game in MLB Gameday and I notice that along with MPH on every pitch (and that great pitch location frame), I see an "NF" number. WTH? (What the HECK)?

It turns out that NF is "Nasty Factor." Have I been living under a rock or is this new?

MLB.com explains it thusly:

The Nasty Factor evaluates several properties of each pitch, and rates the "nastiness" of the pitch on a scale from 0-100, based in part on the success or failure of opposing hitters against previous similar pitches. The Nasty Factor incorporates several different factors for each pitch, including:

Velocity — The greater the pitch’s velocity — as compared to that pitcher’s and the league’s range of speed for that pitch type — the greater the nastiness;
Sequence — The more the pitcher mixes up his pitches, the greater the nastiness… and certain pitch sequences are nastier than others, too;
Location — The closer to the edges of the strike zone is, the greater the nastiness, while pitches closer to the middle of the plate, and farther away outside the strike zone, decrease in nastiness;
Movement — The more movement the pitcher applies to the pitch — as compared to that pitcher’s and the league’s range of movement for that pitch type — the greater the nastiness.

The Nasty Factor also adjusts for how often the pitcher has faced the current batter during the game, as well as how often he has used the same pitch type against the same batter in the current at-bat and previously in the game.

OK, sounds reasonable. What I still don't get is, this is all done instantaneously, by computer? It has to be in order to be listed in Gameday so quickly, pitch by pitch.

Anybody buy into this? Is this a widespread stat or just something MLB.com has cooked up?

[Kobie]

It's something MLB started using a couple of years ago. 2010 was the first year that MLB had it on its gamecasts.

Does Nasty Factor Tell Us Anything? - Lookout Landing

This is a pretty good article on it. It's certainly not widespread by any means.