Deliberate mistake: Several of the matches Nacho loses, he should actually have won. In Mexican pro wrestling, it is illegal to rip another's mask off, and results in immediate disqualification. This happens twice to Nacho, both in the fight with the midgets and in the final against Ramses.
Deliberate mistake: When Zoom is moving the documents from the desk to the floor for Marsha to pick up, she quite blatantly catches him two or three times, but continues on with her business.
Deliberate mistake: At the start of the film when the commentators are explaining the tie situation between the 3 cars the green arrow to the car is out of alignment and misses the car, instead pointing at the track. Pixar Creative Director, Jay Ward, who is this film's team manager (as well as art coordinator) has stated that this was deliberately done as a joke, for fun. It's a little bit off, in the same way that Chick Hicks is a little bit off. This is the video with Jay Ward explaining: https://youtu.be/ZkJre-eC-zE?t=25.
Deliberate mistake: The Benchwarmers originally had only three players, and then only one who could actually hit. Despite this, none of the (supposedly competent) little league coaches chose to simply walk all the players and force an out.
Deliberate mistake: At the end, there is no way that the RV managed to roll over and flatten the vehicles in its path.