Marcelo Bielsa is a coach who likes to dominate games through ball possession. This is why, when Leeds lost the ball, players activated fast, pressed aggressively the ball possessor and ensured the passing lines near the possessor were blocked. This concept, known as counter-pressing, is very important in Bielsa's philosophy and has been applied with high success during his stay at Leeds and previously with other team he managed. In the images below, we can see how James (#20) and Forshaw (#4) press Bruno Fernandes (#18), not allowing him to turn or to pass to any teammate. This allows them to recover the ball quickly and score.
Continuing with the defensive part, there are two key concepts for Marcelo Bielsa in this phase: individual markings and defending the wall-passes. Starting with the first one, it has been a distinctive characteristic of Bielsa's teams throughout all his career. Players are given very specific order to follow their opponent all the pitch. This allows very aggressive defending when an opponent player receives the ball, as he will always have a defender behind him, not allowing him to turn.
Linked to the previous concept, in Bielsa's game model it is of vital importance how their players defend the wall-passes. The reason is that when pressing man-to-man, if one of the players loses their mark, an unbalance is created immediately in the defending team which could easily lead into a clear chance. This is why Bielsa has studied during years how to teach his players the best way of defending the wall-pass (in the video you can see a training drill he used during his time as a national coach of Chile) and his players have a very clear idea on what to do in these situations: follow the player and not the ball.