I'm writing in the wake of Barcelona taking a sledgehammer to AC Milan's metaphorical bus. Milan tried to defend deep, counter, and wait the game out, but ended up on the wrong end of a 4-0 thrashing. Messi and Iniesta ran the show, finding pockets of space and slicing open Milan's defense time and time again. Parking the bus isn't a new strategy, and it's one that Inter and Chelsea both successfully employed in defeating Barcelona and eventually claiming the Champions League title.
First of all, allow me to define what it actually means to "park the bus". It's an ultra-defensive strategy, involving defending with nearly your entire team (or, in Chelsea's case, the entire team). You allow the other team possession, in exchange for occupying almost all available space in your defensive third, keeping the other team from creating any real chances at goal. Then, once they force something and turn the ball over, you counter as fast as you possibly can. Generally, you counter using a fast winger or wingers and a target forward, like Ramires and Drogba, without committing too many men forward.
Parking the bus isn't generally a recipe for a winning team, since you create very few chances for yourself, while allowing your opponent to continue trying to score. Even if all they get is five or six half-chances, that's better than your one or two. It usually forces teams to take outside shots or simply lob crosses into the box, chances that don't carry a good conversion rate, but even one goal and the strategy's ineffective. So, why is this strategy employed against Barcelona?
Barcelona have dominated, and continue to dominate, European football like no other club. They enjoy unprecedented success, brought on by a unique possession style of football, and employed by one of the greatest goal scorers and some of the most creative midfielders football's ever seen. This possession style restricts the opportunities opponents create, while Barcelona simply feels for a seam in the opponents defense and quickly slicing it open. That style creates the most deadly attack in the world, but also the most susceptible one to bus parking.
Before Barcelona's Champions League date with Celtic, Celtic manager Neil Lennon said, simply "they are the best in the world at keeping possession. They dominate to the point it's 70-30." As you'd expect, it's hard to create chances when you only have the ball for 30% of the match. Barcelona maintain possession by passing up half-chances, only taking risks where the payoff is the greatest. When they don't have possession, they press high up the pitch, forcing the opponent into quick turnovers. They dominate teams that try to play them straight-up because the other team can't advance the ball against their press, and higher players leave more gaps open in the back for Barcelona to exploit. So, they sit back, allow Barcelona a little more possession than they normally have anyway, and hit them on the break, the hardest situation to press and defend.
Barcelona struggle against defensive teams because their attack, generally, is one-dimensional. They short-pass teams to death, and finish chances with finesse shots at short range. This attack is precisely what parking the bus aims to stop. They force Barcelona to take long shots, something they're not especially good at. They force Barcelona to cross and win aerial battles, something they're even worse at. Barcelona responds by passing up these opportunities, passing the ball side-to-side until something opens up. Odds are, nothing does. So, they default to Messi and hope he'll create something. Chelsea kept him relatively quiet by playing with two central defensive midfielders, cutting off passing lanes unless he dropped deeper, so he ended up in less dangerous positions. That's a recipe for a blunted Barcelona attack.
Offensively, teams don't suffer simply because they don't lose anything. Barcelona can't press when Ramires is sprinting 80 yards down the right flank with the ball, and shooting the first chance he gets. If they build up patiently, they often end up with no chance at all due to relentless pressure. The thought process is a handful of half-chances is greater than one real chance.
What was unique about Milan's bus? Honestly, nothing. What changed was Barcelona's approach. They played David Villa as a classic number nine (striker) for the first time in two years, to my knowledge. Instead of Messi playing striker and being boxed in by two center-halves and two defensive midfielders, Villa stepped in and forced them to account for him. He plays off the back line, pushing it back and creating more space underneath. Furthermore, they started Pedro out wide, who sticks to the touchline and draws out the fullback more, creating more space. Iniesta and Messi ran the show because of the space this created. Villa's also more of an aerial threat, so if Milan would have backed the center more, Barcelona could cross with more success. They simply didn't need to today.
Parking the bus demands the other team's central striker to change the game, but Villa's more than capable of doing so. Rafa Benitez seems fond of this strategy, and Chelsea's seen more and more opponents utilize it, so it's important for Chelsea fans to understand the pros and cons that go along with it. Drogba's off on Galatasary, so Demba Ba and Fernando Torres need to step up against bus parking teams by keeping the center backs withdrawn, and Moses and Hazard need to force the fullbacks out wide. Then, maybe we can take a sledgehammer to Stoke's team bus.