My favourite is the 1986 European Cup Final. With the game drawn and going into ET, Venables takes him off. Best player Barca had, the only one likely to break the deadlock, but no Venables takes him off. He was probably trying to make it clear who was boss, which was the ongoing problem.
Problem is, as well as the most likely game-changer, Schuster was their designated penalty taker, the one you would give the all important first peno to... He was German for Christ's sake!... and he takes him off the pitch. Nutter. Schuster leaves the pitch in a strop, then the stadium and gets on a cab. The Sevillan cabbie looks through the rearview mirror and turns around, completely startled: "aren't you supposed to be in there playing?". Schuster's face must have been a picture.
Cabbie drives off and with the radio on Schuster listens on, probably with a cnutish knowing smirk on his face, as Barca miss all four of their penos (the worst part being Steaua also missed their first two, so getting the first one in would have made a massive difference). Of course, stupid as Venables was, Schuster made him the winner on the day with his actions. Venables' and the Board's problem was the fans loved their temperamental genius, but walking out on the team like that broke the camel's back, which led to Venables being able to have him spending 1986-87 playing reserve team football.
I've read both sides of the story and as much as I hate it, I think the fault lies fair and square with Schuster on this instance.
I read a segment of Veneables biography, Born to manage and they both reached a gentleman's agreement that Schuster would be allowed to leave at the end of the season. Then Schuster came to training the next day and claimed that he wanted to leave immediately.
Veneables knew this was the work of Gaby and arranged a meeting with her, in which they again agreed that he'd leave at the end of the season but grudgingly so.
On the final, Schuster was subbed and Veneables claims Schuster was unmotivated and had to be removed. Schuster claims he was subbed off as Veneables wanted to show that he could win the CL without Schuster. I'm actually inclined to believe Schuster on this, as it makes sense given their fall out and his impending departure.
However, Schuster made a huge mistake leaving the stadium as there was a random drug test after that match and Veneables had made it clear that everyone had to be present for it.
Luckily for Barca he wasn't one of those who was going to be tested. Veneables was naturally angry and imposed a one year suspension on him (the duration Barca would have been banned from the CL if Schuster was supposed to be tested). Schuster asked to leave but Veneables claimed, why should I honor our agreement when you didn't honor my word or something along those lines.
So Schuster criminally wasted an entire prime year of his career, in the reserves despite many big teams being after his signature. Curiously enough, Veneables also states that Schuster was professional and trained hard in every training that year, despite knowing that he wouldn't feature. The fans also clamoured for his return but Barca and the board stood firm. Just a shame really.
Obviously Veneables could have been spouting nonsense, and telling his side of the story. So events could be skewed or misrepresented.