In basketball, you bet the over and the teams both throw up more bricks than a subdivision. Then you bet the under, and both teams are making circus shot after circus shot that they couldn't make again if they tried? And could care less about playing defense.
In baseball, you bet the under and both teams are getting seeing eye hits, bloops to fall, good pitchers are getting destroyed by batters under the mendoza line, and bullpen pitchers who have no business being in the bigs give up multiple runs? Then you bet the over and great hitters have off nights, defenses make amazing catches and pitchers with sky high eras go out and look like Cy Young.
In football, you bet the under and teams can't tackle, QBs who are backups at best turn into the 2nd coming of Dan Marino and normally strong defenses couldn't stop a nosebleed, kickers make 60 yard field goals. But then you bet the over and receivers have hands made of bricks and butter, and QBs who are normally strong couldn't hit water if they fell out of a boat, and kickers miss extra points and chip shots.
In hockey, you bet the over and goalies make acrobatic stop after acrobatic stop to where you wonder if they broke their spine, no one can convert a power play and players miss wide open shots at point blank range. Then you bet the under and the goalies are so bad they couldn't stop a bowling ball with their leg pads and players have no self discipline so we see power play after power play.