The pitcher shall not --
(a)(1) Bring his pitching hand in contact with his mouth or lips while in the 18-foot circle surrounding the pitching rubber. EXCEPTION: Provided it is agreed to by both managers, the umpire, prior to the start of a game played in cold weather, may permit the pitcher to blow on his hand.
PENALTY: For violation of this part of this rule, the umpires shall immediately call a ball. However, if the pitch is made and a batter reaches first base on a hit, an error, a hit batsman or otherwise, and no other runner is put out before advancing at least one base, the play shall proceed without reference to the violation. Repeated offenders shall be subject to a fine by the league president.
(2) expectorate on the ball, either hand or his glove;
(3) rub the ball on his glove, person or clothing;
(4) apply a foreign substance of any kind to the ball;
(5) deface the ball in any manner; or
(6) deliver a ball altered in a manner prescribed by Rule 8.02(a)(2) through (5) or what is called the shine ball, spit ball, mud ball or emery ball. The pitcher is allowed to rub the ball between his bare hands.
I saw only the final inning of Mike Fiers' no-hitter and wasn't on Twitter at the time, but apparently there was a little uproar over the suggestion that the Houston Astros right-hander had a foreign substance -- pine tar? spray-on sunscreen? -- in his glove. Matthew Kory has a good look at the controversy at FanGraphs. Actually, I guess it wasn't much of a controversy, since the Dodgers didn't seem to raise any ire after the fact.
Kory's piece includes an incriminating screen grab that shows a shiny substance on the inside of Fiers' glove, which would be a clear violation of Rule 8.02 (a), which mandates an automatic 10-game suspension.
Two things here: Applying a foreign substance to the ball seems to be an accepted part of the game, unless you're clearly and obviously violating the rule, such as Michael Pineda did last season with the Yankees, when his neck was shiny with goo. Also, hitters don't seem to care all that much about the issue, saying they'd rather have the pitcher get a good grip on the ball than firing a slippery baseball that may drift up and in.
Did Fiers do anything different on Friday? Kory investigates whether Fiers was getting more movement on his pitches. Kory writes,
"As you can see, Fiers' cutter typically moves horizontally about two inches and that's roughly what it did during the no-hitter. Vertically though was a different story. Fiers' cutter moved over two inches vertically more (i.e. with extra "rise" relative to a spinless ball) than it has done typically this season. If Fiers was using something to help him throw a better cutter, you’d expect him to throw it more frequently than he usually does, too, right? Well, he did. Fiers threw his cutter just over 17% of the time during his no-hitter. Compare that to the 8.9% of the time he has thrown his cutter otherwise and you have ... well, something. Of course, if Fiers weren't cheating and just had a better cutter that day due to feel or whatever other perfectly legal reason, you'd also expect him to throw it more frequently."
As Kory suggests, the data is only relevant if Fiers was doing something illegal on Friday and hadn't done anything illegal prior to his no-hitter. In other words, there's too much unknown about the data to draw any conclusions. Bottom line: Until teams starting making an issue of foreign substances, it's a non-starter; but since pitchers on every team are likely using something to improve their grip, you're not going to see that happen.