Okay, here is a VERY recent example of a baseball bat effectively used for self defense against a knife:
http://www.ketv.com/news/9554485/detail.html
...Konfrst said he also saw the knife, so he pulled a baseball bat out of the back seat...
..."When I was coming around the car, the guy had grabbed Casey by the hair and took and threw her back at the car," Konfrst said. "He threw me against my car door, told me to get the hell in my car."
Konfrst said the woman came at him. He said she jabbed at him, then stuck the knife in the back left tire.
"That showed me she had plenty of intention of stabbing something," Konfrst said.
So he hit her with the bat, and the male accomplice tried to rip off the car antenna and came at him, the victimized couple said.
"I hit him the first time, and he was coming at me still, acting like he was going to attack me. So I stepped back and hit him again, and he fell," Konfrst said.
The suspects drove off in their car. (The suspects were later arrested when they showed up at the emergency ward to get treatment for the man).