I have a DVR through DirecTV (different brand than Tivo, but basically the same thing.)
Any time I am recording a sporting event, I set it to record the following program as well. It records the time block allocated for the game (usually 3:30 for football,) and stops when that time block ends, even if the game isn't over.
It can also get messed up if an earlier game botches up the schedule for the rest of the day, so I now have 2/3 of "Maverick" on my hard drive as well.
Just remember that the DVR doesn't know when the game starts and ends. It knows when the game is supposed to start and end, and it records that channel during that time. To be safe, set it to get the next time block as well, and record that show, even if you are just going to delete it.