Be VERY careful that you not only use the CORRECT footage in your spots. But most of all, make sure you have the RIGHTS to use that footage. You can't just grab any old footage you want and use it...especially sports clips.
GOTTA get the rights. And know that buying it off sites like Pond5 doesn't mean that you automatically have the rights. For example...this clip of Walter Cronkie announcing the death of JFK.
The clip costs $150. But that doesn't give you the rights to the CBS footage of Cronkite on the TV in this clip. NOPE! You have to contact CBS to obtain the rights to that, and pay them even more. This is VERY dangerous.
I see these kinds of mistakes made a lot in non-broadcast "web only" spots, which are sometimes done by less-experienced people. To see it in a broadcast spot is pretty rare, since those go thru more rigorous checking by various lawyers at different points.
Hard to find Mitch's legit spots on youtube right now, as the web searches seem to all point to examples of 'McConnelling", that gag started by The Daily Show, where people substitute various music tracks to go with stock footage of the Senator released by his campaign. The re-edits range from hysterical to darned creepy.