Probably the most misguided rule in football are the caution / booking (yellow card) and sending off (red card).
Although it is necessary to have measures to deal with unacceptable / dangerous behaviour on the field the methods currently available only serve their purpose in a limited manner.
First there is the booking where a player is shown a yellow card. In many cases after injuring an opponent or robbing the opposing team of half chance or goal scoring opportunity. This has little effect on the player concerned and the team he has offended against gain nothing. Perhaps after a few such incidents, another team benefits.
The second is the sending off or red card. This can drastically change a game, especially early on and can be applied with little intent, for example by a goalkeeper being late for a challenge. Many games have simply been ruined by such incidents, the European Champions League final in 2006 between Arsenal and Barcelona being an example.
It also means that referees can be reluctant to produce a red card, knowing it will change the match dramatically. An example that comes to mind is the 2010 World Cup final between Holland and Spain.
A better way can be found in other similar sports, team handball for example.
These rules could be applied to football so that a yellow cards should include 5 minutes off the field where a team has to play with reduced number of players. After that, the player can be introduced back on the field.
And similarly, a red card would mean 15 minutes suspension where the player’s team plays with fewer players, but after that a substitute can replace the red-carded player.
In extreme cases, for excessive violence, a no-substitutable red card could be used, but this should be rare enough to happen only once in two or three seasons for all teams and leagues.