X factors for each UEFA Champions League quarterfinal team - ESPN

It might seem like there are clear favorites in each Champions League quarterfinal matchup, but based on the betting odds, there's only about a 1-in-5 chance that Real Madrid, Bayern Munich, Paris Saint-Germain and Barcelona all advance.

That's because a lot can happen across 180 minutes of knockout soccer.

Optimal tactics, systems, strategies, roster quality, talent depth are the things that win you league titles. But over just two matches, individual performances and stylistic dynamics matter more than anything else.

Two underwhelming matches from your star winger, and suddenly you're sitting at home. A blinder from your backup fullback? Here's your ticket to the semifinals.

So, ahead of the first legs of the four remaining matchups kicking off Tuesday and Wednesday, let's take a look at the players, people and philosophies that might have an outsize effect on who punches through to the semifinals.

Here are your eight X factors for the UEFA Champions League quarterfinalists:

Arsenal's quarterfinal matchup is Real Madrid, a team for which the players have changed some but the performances haven't over the past five years. They still have an incredible amount of attacking talent that frequently underperforms but also has an uncanny ability to elevate in the highest-leverage moments of matches.

Defensively, it's kind of just vibes, hoping players make plays while trusting in Thibaut Courtois. Among the remaining teams, only Aston Villa allows a higher opposition pass-completion rate and presses less aggressively (as measured by passes allowed per defensive action) than Madrid. And only Villa and Dortmund allow more shots per game, goals per game and expected goals per game.

Madrid, in particular, seem to struggle with