I have a player (8188859) who plays between 55 and 70 min per week and his stamina dropped this week so I wonder 1 - why does it drop if a player is playing say 30 min a game ? and 2 - how do you increase stamina ? thanks
Because BBs are bad people, so they created a skill which drops a little random amount every week irrespective of the minutes played. There is nothing to do with it except to buy a Specialist Trainer who decreases this amount.
The only way to raise it is to train it.