Question: What position did the man who became the manager of Middlesbrough mainly play?

Context paragraphs:
Craig Liddle: Craig George Liddle (born 21 October 1971) is an English former footballer who made more than 300 appearances in the Football League playing for Middlesbrough and Darlington, where he spent most of his professional career.  His predominant position was as a central defender.  He is currently Academy Manager at Middlesbrough.

Ehime Mandarin Pirates: The Ehime Mandarin Pirates (愛媛マンダリンパイレーツ , Ehime Mandarin Pairētsu ) are a professional baseball team in the Shikoku Island League Plus of Japan.  Established in 2005, the Mandarin Pirates mainly play their home games at Botchan Stadium in Matsuyama, the capital city of Ehime Prefecture.

Aitor Karanka: Aitor Karanka de la Hoz (] ; born 18 September 1973) is a former footballer who played mainly as a central defender (on occasion, he occupied the left back position), and a current manager.

Indonesia XI: Indonesia XI (also known as Indonesia XI, Indonesia Selection, or Indonesia League Selection) is a football team which represents the Indonesia League in matches.  Indonesia XI mainly play Non FIFA 'A' international match mostly against clubs while the competitive matches such as World Cup Qualifiers and the Asian Cup are played by the Indonesia national football team

Barrie Stimpson: Barrie George Stimpson (born 8 February 1964 in Billingham) is an English former professional footballer and former non-league manager.  Stimpson now spends his weekends following Middlesbrough Football Club up and down the country, in 2015 he became Vice President of the North Lancs South Lakes Middlesbrough supporters club (NLSLMSC).  He played as a full-back, including Football League appearances for both Hartlepool United and Chesterfield.

Tokushima Indigo Socks: The Tokushima Indigo Socks (徳島インディゴソックス , Tokushima Indigo Sokkusu ) are a baseball team in the Shikoku Island League plus of Japan.  Established in 2005, the Indigo Socks mainly play their home games at Tokushima prefecture Kuramoto stadium in Tokushima, Tokushima Prefecture.

Al-Ahli Club (Manama): Al-Ahli Club of Manama (Arabic: النادي الأهلي البحريني‎ ‎ ) is a Bahraini sports club based in the capital city of Manama.  They used to play in the top division in Bahraini football but were relegated to the second division after finishing ninth in the 2011–12 First Division league.  The club also fields players in other sports such as basketball, handball, and volleyball.  Their home stadium is Al Ahli Stadium, although like all other teams in Bahrain they mainly play on Bahrain National Stadium.

Malaysia League XI: Malaysia Super League All Stars (also known as MSL All Stars, Malaysia Selection, or Malaysia League Selection) is a football team that represents the Malaysian League in exhibition matches.  Malaysia XI mainly play non-FIFA 'A' international matches while the competitive matches such as World Cup Qualifiers and the Asian Cup are played by the Malaysia national football team.

2013–14 Middlesbrough F.C. season: The 2013–14 Season is Middlesbrough's fifth consecutive season in the Championship.  They also competed in the League Cup which they were knocked out by Accrington Stanley in a 2–1 defeat and will also compete in the FA Cup.  Following a poor run of form, the defeat to Barnsley saw Tony Mowbray's tenure at the club end on 21 October 2013.  Following this announcement, his assistant manager Mark Venus took charge as caretaker manager.  On 13 November, José Mourinho's former Real Madrid assistant Aitor Karanka signed a 2 ⁄ -year deal to become manager of Middlesbrough.

Stephen Ackles: Stephen Ackles (born 15 February 1966), son of Norwegian mother (Bergliot Kittilsen) and American father (Allan Dale Ackles) is a beloved Norwegian vocalist, pianist, and songwriter who mainly play rock 'n' roll inspired by Jerry Lee Lewis, Chuck Berry, Little Richard, Elvis Presley with several.

Supporting paragraphs: 2013–14 Middlesbrough F.C. season Aitor Karanka
Answer: central defender