Question: what position did Ömer Toprak play for Borussia Dortmund

Context paragraphs:
Borussia Dortmund: Ballspielverein Borussia 09 e.V. Dortmund, commonly known as Borussia Dortmund ] , BVB, or simply Dortmund, is a German sports club based in Dortmund, North Rhine-Westphalia ("Borussia" is the Latin equivalent of Prussia).  The football team is part of a large membership-based sports club with more than 145,000 members, making BVB the second largest sports club by membership in Germany.  Dortmund plays in the Bundesliga, the top tier of the German football league system.  Dortmund is one of the most successful clubs in German football history.

Borussia Dortmund II: Borussia Dortmund II is the reserve team of Borussia Dortmund.  It plays in the Regionalliga, at Stadion Rote Erde.  Until 2005, the team played as Borussia Dortmund Amateure.

2017–18 Borussia Dortmund season: The 2017–18 Borussia Dortmund season is the 109th season in the football club's history and 42nd consecutive and 51st overall season in the top flight of German football, the Bundesliga, having been promoted from the 2.  Bundesliga Nord in 1976.  In addition to the domestic league, Borussia Dortmund also are participating in this season's editions of the domestic cup, the DFB-Pokal, and the first-tier continental cup, the UEFA Champions League.  Dortmund are the reigning DFB-Pokal champions, and therefore also are participating in the German super cup, the DFL-Supercup.  This is the 44th season for Dortmund in the Westfalenstadion, located in Dortmund, North Rhine-Westphalia, Germany.  The season covers a period from 1 July 2017 to 30 June 2018.

Borussia Dortmund in European football: Ballspielverein Borussia 09 e.V. Dortmund, commonly known as Borussia Dortmund ] , BVB, or simply Dortmund, is a German sports club based in Dortmund, North Rhine-Westphalia ("Borussia" is the Latin equivalent of Prussia).

2016–17 Borussia Dortmund season: The 2016–17 Borussia Dortmund season is the 106th season (and 107th overall year) in the football club's history and 41st consecutive and 50th overall season in the top flight of German football, the Bundesliga, having been promoted from the 2.  Bundesliga in 1976.  In addition to the domestic league, Borussia Dortmund will also participate in this season's editions of the domestic cup, the DFB-Pokal, and the first-tier continental cup, the UEFA Champions League.  This will be the 44th season for the club in the Westfalenstadion, located in Dortmund, Germany.  The stadium has a capacity of 81,360 for Bundesliga matches, and a capacity of 65,851 for continental matches.  The season covers a period from 1 July 2016 to 30 June 2017.

Shinji Kagawa: Shinji Kagawa (Japanese: 香川 真司 "Kagawa Shinji" ] ; born 17 March 1989) is a Japanese professional footballer who plays for German club Borussia Dortmund and the Japan national team.  Kagawa began his professional career in his homeland with Cerezo Osaka before joining Borussia Dortmund in 2010.  After two years with Dortmund, Kagawa signed for Manchester United on a four-year contract.  Two years later, he returned to Dortmund.  A goal-scoring midfielder, he is known for his "vision, technique, movement and deft passing."  Kagawa holds the records for most appearances and goals by a Japanese player in UEFA club competitions.

Ömer Toprak: Ömer Toprak (born 21 July 1989) is a Turkish professional footballer who plays as a centre back for German club Borussia Dortmund and the Turkey national team.

2015–16 Borussia Dortmund season: The 2015–16 Borussia Dortmund season is the 105th season (and 106th overall year) in the football club's history and 40th consecutive and 49th overall season in the top flight of German football, the Bundesliga, having been promoted from the 2.  Bundesliga in 1976.  In addition to the domestic league, Borussia Dortmund will also participate in this season's editions of the domestic cup, the DFB-Pokal, and the second-tier continental cup, the UEFA Europa League.  This will be the 43rd season for the club in the Westfalenstadion, located in Dortmund, Germany.  The stadium has a capacity of 81,359 for Bundesliga matches, and a capacity of 65,851 for continental matches.  The season covers a period from 1 July 2015 to 30 June 2016.

1997 UEFA Super Cup: The 1997 UEFA Super Cup was a two-legged football match played on 8 January 1998 and 11 March 1998 between Borussia Dortmund of Germany, winner of the 1996–97 UEFA Champions League and Barcelona of Spain, winner of the 1996–97 UEFA Cup Winners' Cup.  Barcelona won the match 3–1 on aggregate, beating Borussia Dortmund 2–0 at Camp Nou in the first leg and drawing the second leg 1–1 in Westfalenstadion, Dortmund.

Borussia Dortmund (Superleague Formula team): Borussia Dortmund Superleague Formula team was the racing team of Borussia Dortmund, a football team that competes in Germany in the Fußball-Bundesliga.  The Borussia Dortmund racing team competed in the Superleague Formula.  They were operated by former Formula One team Zakspeed.  They did not return for the 2009 season.

Supporting paragraphs: Ömer Toprak Borussia Dortmund
Answer: centre back