Diego Costa can't win.

Before he decided which national team he'd play for at the World Cup, the 25-year-old Brazilian-born Spanish striker was the target of nationalistic taunts from fans.

"Diego Costa is not Spanish!" Real Madrid supporters chanted during a game in September.

After he decided to play for Spain, an outraged Brazilian football federation went a step further than those Madrid fans. They declared that Costa should be stripped of his Brazilian citizenship. At World Cup training in Brazil, fans taunted Costa with taunts of, "Traitor! Traitor!"

Costa became the most sought-after center forward in the world on both the club and international level this season. He scored 36 goals in all competitions for Atletico Madrid, leading them to the Champions League final and a deep La Liga title run.

With the eligibility to play for both Spain and Brazil, he found himself in the middle of a tense tug-of-war between the two best teams in the world.

Costa making his Spain debut.

He played in two friendlies for Brazil in March of 2013, but never appeared in an official FIFA game that would have tied him to the team for life. In July — at the same time Brazil was playing Confederation Cup games without him — Costa got a Spanish passport after living there for five years while playing professionally.

A few months later, amid a hot start to the season in La Liga, Spain began recruiting him to make a dramatic national team switch on the eve of the World Cup.

In an interview in March, Costa admitted that Spain wasn't even on his radar at this time last year:

"I never imagined it. When I heard there was interest from Spain I began to imagine things, to think: ‘Why not?’"

He made his decision official in October, infuriating Brazil in the process, and stepped onto the field in a Spanish shirt for the first time in a March 2014 friendly — almost exactly a year after doing the same thing for Brazil.

Brazil's federation said he should be stripped of his citizenship and accused him of making the switch for money.

Brazilian coach Luiz Felipe Scolari released a strongly worded statement saying, basically, that Brazil wouldn't want a traitor like him anyway:

"A Brazilian player who refuses to wear the shirt of the Brazilian national team and compete in a World Cup in your country is automatically withdrawn. He is turning his back on a dream of millions, to represent our national team, the five-time champions in a World Cup in Brazil."

We see dual citizens change allegiances all the time. But Costa's case is special. He's one of the best players in the world, both teams have holes at his position, and he switched in a World Cup year.

Brazil has a strong back line and a bevy of creative midfield players. Their lone weakness is the lack of a focal point at striker — something Costa would have been perfect for.

Spain, on the other hand, may have found a solution to their striker problems in Costa. While they've been the most dominant team in the world in the last six years, they've done it without a consistent presence up top. During the 2012 Euros, they even deployed a false 9 — a striker-less formation.

Costa is just what Spain needs.

Still, though, there's the impression that he hasn't been fully embraced by Spanish fans.  He's the type of player you love when he's on your team but hate when he's on the other team .

Spanish soccer writer Side Lowe summed up his game nicely in an article last year:

"Costa is a tough, aggressive player. One of the words that is often used to describe him is 'jailhouse.' He winds people up and gets wound up back; as one newspaper put it, he has 'arms like a Swiss Army Knife.' He never pulls out of a tackle, he bullies defenders and he doesn't mind pulling a dirty trick or two. He is good at what in Spain is sometimes called 'the other football.' Costa came into this season having already picked up 35 yellow cards in his career — only five players in the league have committed more fouls than him this season."

He gets yellow cards. He mixes it up with opponents. He snubs Brazil and offers a somewhat flip "Why not?" as an explanation.

He might also shift the tide of the World Cup.