Question: Who played as a forward for Premier League club Arsenal and began his career at Southampton F.C. Under-23s and Academy?

full_context: Document 1: Norwich City F.C. Under-23s and Academy: Norwich City Under-23s and Academy is the youth organisation run by Norwich City. The team is made up of under-23 and academy players and is effectively Norwich City's second-string side, but is limited to three outfield players and one goalkeeper over the age of 23 per game following the introduction of new regulations from the 2012–13 season. The under-18 players among other younger age groups make up the academy team.
Document 2: Ashley Young: Ashley Simon Young (born 9 July 1985) is an English professional footballer who plays as a winger for Premier League club Manchester United and the England national team.
Document 3: Alex Oxlade-Chamberlain: Alexander Mark David Oxlade-Chamberlain (born 15 August 1993) is an English professional footballer who plays as a midfielder for Premier League club Liverpool and the England national team.
Document 4: Swansea City A.F.C. Under-23s: Swansea City Association Football Club Under-23s is the most senior team of Swansea City's youth teams and are the club's former reserve team. From the 2015–16 season, they will play in Division 2 of the Professional Development League 1 and will also compete in the U21 Premier League Cup. The Under-21s and Under-18s previously played in the Professional Development League 2 South Division. The Under-21s play the majority of their home games at Swansea City's Youth Academy in Landore, Swansea with occasional matches taking place at the Liberty Stadium.
Document 5: Aston Villa Under-23s and Academy: The Aston Villa Under-23, formerly Aston Villa Under-21 and Aston Villa Reserves, are the most senior youth development team of Aston Villa and compete in Premier League 2 (Division 2) of the Professional Development League and the Premier League International Cup in the 2016–17 season. The team were part of the FA Premier Reserve League since its foundation in 1999 and were winners of the 2011-12 Premier Reserve League South title, the last in that format. The team plays its home games at Villa Park and Bescot Stadium (home of Walsall F.C.). Aston Villa also have an academy side that competes in the Under-18 division of the Professional Development League and the FA Youth Cup annually.
Document 6: Theo Walcott: Theo James Walcott (born 16 March 1989) is an English professional footballer who plays as a forward for Premier League club Arsenal and the England national team.
Document 7: Andros Townsend: Andros Darryl Townsend (born 16 July 1991) is an English professional footballer who plays as a winger for Premier League club Crystal Palace and the England national team.
Document 8: Jermain Defoe: Jermain Colin Defoe (born 7 October 1982) is an English professional footballer who plays as a striker for Premier League club Bournemouth and the England national team.
Document 9: Danny Welbeck: Daniel Nii Tackie Mensah Welbeck (born 26 November 1990) is an English professional footballer who plays for Premier League club Arsenal and the England national team. He primarily plays as a forward but can also play as a winger.
Document 10: Chelsea F.C. Under-23s and Academy: Chelsea F.C. Under-23s are the under-23 team of Chelsea Football Club. They play in the Premier League 2, which is the top level of reserve football in England. They were the Champions in the 2013–14 season. The team mainly consists of under-21 players at the club, although senior players occasionally have an appearance, for instance when they are recovering from injury. The under-23 team is coached by Joe Edwards.
Document 11: Watford F.C. Under-23s and Academy: Watford F.C. Under-23s and Academy is the youth setup of Watford. The Under-23 team is effectively Watford's second-string side, but is limited to three outfield players and one goalkeeper over the age of 23 per game following the introduction of new regulations from the 2012–13 season. They play in Premier League 2 Division 2 and also compete in the Checkatrade Trophy. The Under-18 side is the most senior team in the Academy.
Document 12: Marcus Rashford: Marcus Rashford (born 31 October 1997) is an English professional footballer who plays as a forward for Premier League club Manchester United and the England national team.
Document 13: Southampton F.C. Under-23s and Academy: Southampton Under-23s and Academy or Saints Under-23s and Academy is the youth organisation run by Southampton F.C. to encourage and develop young footballers in the south of England. Renowned players including Gareth Bale, Theo Walcott, and Alan Shearer began their careers at this academy.
Document 14: West Ham United F.C. Reserves: The West Ham United Academy is recognised as one of the most successful academies in modern football, hence its nickname the Academy of Football. The introduction of the FA's new Academy system in 1998 has placed even more emphasis on the developing of young homegrown players and today the youth system at West Ham is more important than it has ever been. With the influx of many foreign players in the Premier League during modern times, West Ham United has been regarded as one of the few remaining clubs in top flight to continue producing and playing homegrown English players.
Document 15: West Ham United F.C. Under-23s: West Ham United F.C. Under-23s, formerly West Ham United F.C. Under-21s is the most senior of West Ham United's youth teams. The Under-23 team is effectively West Ham United's second-string side, but is limited to three outfield players and one goalkeeper over the age of 23 per game following the introduction of new regulations from the 2012–13 season. They play in Premier League 2 and also compete in the Checkatrade Trophy.
ground_truth: Theo Walcott