When the game matters to the team, they need to go forward, while at the same time the opponents start to infringe by defending the goal in every way they can. It is common to see "amateurs" stalling in the final minutes, for which they are penalised with "mustard penalties", especially for goalkeepers. When there is no motivation, offences are minimised and the game runs smoothly. Let's compare some of the semi-finals of the European Championships. The desire and will to reach the final was enormous.
Referees penalise defenders more often
The job of the defenders is to prevent the opponents from creating a scoring chance. They take a position that forces them to take the ball away, breaking off in the worst case if they can't keep up with the fast players.
Let's compare the position that was penalised more often as a yellow in the 2017-2018 season on the betwinner website - you can see the statistics of players and teams by cards. The table shows the percentage of yellow cards by position in Europe's top leagues.
The outsiders get more yellow cards
In a particular case, the team that is "sitting" in defence, possesses the ball less than 44%, has a lower class of players and commits infringements. When one club has a superiority of players: technique, speed, accuracy, the opponent tries to resist at the expense of small fouls, hence receives a warning.
An example of a 2015/2016 Champions League group stage match between BATE and Barcelona.