Wooster,
"Slippery Rock" was a creation by a whim of Cactus' brother Wally, who was the Memorial Stadium play by play announcer. Found a Daily Texan article from 1975 with comments about it by Wally:
Austin Daily Texan Newspaper Archives, Nov 14, 1975, p. 17
"It all started when I read a Slippery Rock score that I received off Western Union," Pryor said. "Well a few people laughed, but I didn't think much about it. The next week I forgot to read their score and received about 15 calls wanting to know how Slippery Rock fared. After that I started correspondence with them, and the friendship has become a close one."
P.S., for us OGs, check out other pages of the Texan in the link above, like p 21/34 (click on the L/R arrows and note page number in top info row):
Rome Inn, 10 cent draft beer with meal,
p 27/34: Pleasure Time Beverages beer prices, ex.: cases of longnecks (returnables), e.g., Lone Star $4.29 (that's a CASE), Shiner $3.88 (probably Shiner Premium, would have said Shiner Bock in 1975 if so,
p 32/34 apartment ads, e.g., La Paz 1 BR, furnished, $165/mo.,
p 33/34 Armadillo World Headquarters was still doing its thing,
backwards,
p 16/34, Sizzler, Steak and King Crab, WAS $3.49, now $2.99,
p 13/34 for the sake of this thread, photos of the Union near completion,
and of course, p 12/34, Pancho's all you can eat buffet, $1.79!!