Watch Zack Greinke steal second base with a dangerous headfirst slide

The Arizona Diamondbacks didn't sign Zack Greinke to a six-year, $206.5 million contract for his speed. And they'd certainly prefer he not slide headfirst.

Still, it made for an entertaining moment when Greinke stole second base against the Colorado Rockies on Thursday night -- reaching a maximum speed of 20.3 mph!

But why is an ace sliding headfirst and risking injury by leading with his pitching hand?

"I don't ever want to slide headfirst," Greinke said. "But for some reason, when I was running, I didn't have good balance and was like almost leaning forward, so it would have been tough to switch my momentum into a feet-first slide. Everything's healthy."

It was Greinke's first steal of the season and the fifth of his career. And manager Chip Hale probably wouldn't mind it being his last.

"I wasn't too happy with that," Hale said. "I don't know where that came from."

Greinke settled for a no-decision Thursday -- snapping a streak of seven consecutive starts with a win -- allowing three earned runs in 5 2/3 innings in the Diamondbacks' 7-6 victory over the Rockies.