My brother found a dedicated Tennis/Hockey console called a Digitek 2001 somewhere and was wondering if he could find out more about it, including what it might be worth. I don't know much about these things but I told him I knew a place I might ask.
It's the console on the bottom right in this pic.
http://userwww.sfsu.edu/~hl/c.tvgames.1.html
It's battery operated and appears to have an antenna out and maybe a headphone or audio jack (the antenna jack is labeled, the other is not). And maybe its own speaker, too, it looks like it. Wasn't able to find much on it online, other than that it was made in 1976 and sold under several other names in other countries, apparently.