If using an Intel Mac, OnTheAir CG from Softron (http://www.softronmedia.com) It uses Blackmagic Design Decklink cards to key CG over live video in standard definition.
I just started hosting the Softron Forum here on the Cow so if you have more questions on Softron, ping me over there and I will answer them in that forum.
If you are using a PC with XP, you can use UltraRed from Magicsoft (http://www.magicsoft.tv) UltraRed uses BMD, BF and Deltacast cards for overlaying video. There are SD and HD versions. Refer to the specs on their site if you are configuring the system yourself.
There are any number of CG apps that will do what you ask for. However, if you are looking for a dedicated sports statistics hardware / software bundle, you might check out the Deltacast Stat system on their website. http://www.deltacast.tv/