Continuity mistake: When the team captain comes in to talk to the coach about giving up his spot for Rudy so Rudy could dress, the coach has a clock/pen and pencil set at the front of his desk. However, when the captain and all the other players lay their jerseys on the desk, the pen and pencil set is gone.
Factual error: The Big Game in Rudy takes place in 1975, which means Rudy started at Holy Cross in 1972. To get to Holy Cross, he takes a bus there. In that touching goodbye scene with his father at the bus station, look at the mural in the back ground. It is a depiction of the New York skyline with the Twin Towers, which were not completed until 1973, after that scene should have taken place.
Revealing mistake: Just before the start of the final game which is supposed to be in December we see several shots of the parking lot where it is snowing cold and obviously winter, but yet just before the game starts the camera shows a wide shot of the stadium where you can see rows and rows of lush green trees in the background.
Factual error: When Rudy first arrives on Notre Dame's campus, he is advised to attend Holy Cross junior college to get his grades up so he can be eligible to attend Notre Dame. According to historical data, Rudy enrolled at Holy Cross in 1972. But in the scene when Rudy first walks onto Notre Dame's football field from the end zone, the Goal Post is at the end of the end zone. NCAA goal posts were not moved to the back of the end zone until 1974, so the goal post should have still been on the goal line in 1972.
Factual error: When Rudy is reading his acceptance letter from Notre Dame, he quotes that he was accepted as a freshman. Earlier in the film, he said to Father Cavanaugh that this was his last chance, because Notre Dame doesn't accept senior transfers. The acceptance letter should have listed him as a junior transfer student.
Other mistake: Rudy continually checks the roster to see if he made the dress list. The captain of the team is Roland Steele; the first one to visit the coach about giving up his jersey for Rudy. Every time Rudy looks at the list he scans past the last names for "S" where you should see Steele, Roland. Steele doesn't appear on the dress list yet he dresses every game. Stock, J. (Capt.) appears on the list, so Steele should too.