St. Louis manager Tony La Russa and pitching coach Dave Duncan both told the St. Louis Post-Dispatch the stain on the bill of Arroyo's cap was pine tar that helped him grip balls during a 6-1 victory Wednesday. Cardinals starter John Smoltz found balls slippery and walked five in four innings.
Duncan said umpires assured him balls were properly rubbed. New baseballs are rubbed by clubhouse attendants with a special mud designed to give pitchers a better grip.
Arroyo said the stain on his cap is residue from mud used to rub baseballs at other ballparks.
"It's from playing in every other park where there's so much mud on the balls that that black stuff comes off on young fingers every time," Arroyo said. "I guess [Duncan] said I went to my hat time after time. Yeah, I do 8,000 other twitches. What you want me to do about it? That's how I pitch.
"I guarantee when I pitch against the Cardinals next year, I'll call over and tell Dave Duncan I'm wearing a brand new hat."
Reds manager Dusty Baker said the Cardinals have their own experience with doctored caps.
"If anybody should know, it would be Duncan," Baker said. "I remember they had Julian Tavarez over there. They threw his hat out, remember that? His hat was all messed up. It's not like it's something new."
Tavarez, then with the Cardinals, was suspended for eight days by Major League Baseball in 2004 for applying a foreign substance to balls during a game against Pittsburgh that Aug. 24.
Arroyo (15-13) finished with 12 consecutive starts in which he went at least seven innings while allowing no more than three earned runs. According to the Elias Sports Bureau, he is the first Reds pitcher since at least 1900 to put together such a streak and only the fourth overall in the last 20 years, joining Greg Maddux (12 straight for the Cubs in 1992), Randy Johnson (14 for Arizona in 1999) and Curt Schilling (12 for Arizona in 2002).