Stamina is absolutely vital for any players who use playmaking. For inner midfielders it's not a secondary skill, but a primary one together with playmaking. One of the most common mistakes by playmaking trainers is to slowly increase stamina for their players. Playmakers with anything below solid stamina are a waste of resources in a league or cup game.
If a player does not have enough stamina, a serious drop in their playmaking contribution will be noticed, particularly during the second half of matches.
The Rules state,
- It's very hard to maintain stamina above the level of "excellent" for a long period of time. All players just above the dividing line between "excellent" and the level under it are successively pressed downwards. There's a limit to how well the human body can perform.
Although it is not stated in the rules, the maximum stamina skill level has been observed to be Formidable. While the rules state that players are "successively pressed downwards," in practice players have been found to hold formidable stamina until either an age-related decline or a stamina training causes the player's stamina skill to update (and be reduced to excellent). This means that if you do stamina training, a player with formidable stamina has about a one in three chance of keeping it.