Putting on a mock fight is a great way to get the audience's attention that doesn't require any props.
If the other team has a mascot, you can talk to him beforehand and make a plan to work together to entertain everyone at the game You can agree that the mascot for the team that's winning will also win the fight or that whoever wins this time will lose the next time you meet.
You can get a great laugh out of the audience by pulling down the outer layer of pants of one of the players while he is standing on the sidelines. Be sure to get the player's permission ahead of time.
You can also have a supersoaker war with a kid in the audience. Plant a number of sizes of water guns out of sight. After you squirt with a tiny gun first, the kid should shoot back with a slightly bigger one. You should shoot back and forth, slowly working up to a huge water gun.
You can keep the crowd interested in your skits by getting them directly involved, even just by pulling them out of their seats to dance or by posing for pictures for them.
You can offer a prize to an audience member who comes down and imitates your dance steps and antics. You can pull off the shoe of one member of a couple and throw it far away, and then sit down next to their date and pretend to flirt when they go to fetch it. You can encourage audience members eating popcorn to try to throw it into your mouth, sometimes pretending it's hitting your eye or causing you to choke.
You can ask a friend to bring a bag or have an assistant plant it in the audience next to someone. Picking it up and miming to the person that you want to borrow it (even if it isn't theirs), you can nonchalantly pull out a number of strange items before pulling out and pretending to use a handkerchief.
Another great way to make your show interesting is to do skits related to things that are current news and events and upcoming holidays. During Christmas, for example, you might play with mistletoe, or you could put on something politically themed during an important campaign. You can also do parody acts of recent popular movies.