Question: What league does the team Billy Houghton made 51 appearances for play in?

Context paragraphs:
Watford F.C.: Watford Football Club is a professional football club based in Watford, Hertfordshire, England, that plays in the Premier League, the highest level in the English football league system.  Founded in 1881 as Watford Rovers, the club entered the FA Cup for the first time in 1886, and the Southern League a decade later.  After finishing the 1914–15 season as Southern League champions under the management of Harry Kent, Watford joined the Football League in 1920.  The club played at several grounds in its early history, before moving to a permanent location at Vicarage Road in 1922, where it remains to this day.  Watford spent most of the following half century in the lower divisions of The Football League, changing colours and crest on multiple occasions.

Russell Milton: Russell Milton (born 12 January 1969) is an English former professional footballer, born in Folkestone, who played as a midfielder in the Hong Kong First Division League for Instant-Dict and scored 14 goals from 117 games in the Football League for Cheltenham Town.  He began his football career as a trainee at Arsenal, and also played non-league football for Dover Athletic and Bath City, for whom he made 51 appearances (40 in the league) and scored three goals.

Emmanuel Bourgaud: Emmanuel Bourgaud (born 25 October 1987) is a French professional footballer who plays for Amiens as a midfielder.  He began his career with Angers in 2005, where he made 51 appearances in Ligue 2, the second tier of the French football league system.  He spent time on loan with Créteil in 2011, before being transferred to Vendée Poiré sur Vie later in the year.  Bourgaud scored a last second goal to promote Amiens SC in the 2016-17 Ligue 2.

Billy Houghton: Billy Houghton (born 20 February 1939 in Hemsworth, Yorkshire) is an English former professional footballer.  During his career he made over 200 appearances for Barnsley, 139 appearances for Rotherham United, over 100 appearances Ipswich Town and 51 appearances for Watford. Started out at Barnsley as a part-time professional having a job in the building trade.

Dave Mossman: David John "Dave" Mossman (born 27 July 1964) is an English former footballer who made 51 appearances in the Football League playing for Bradford City, Stockport County (in two spells) and Rochdale.  He played as a winger.  He began his career with hometown club Sheffield Wednesday, without playing first-team football for them, and went on to play in the Football Conference, for Lincoln City as they won the 1987–88 title, and for Boston United.

John Ince (footballer): John Ince (1908–1968) was an English footballer who made 51 appearances in the Football League playing as a goalkeeper for Darlington and Gateshead in the 1930s.  He was also on the books of Exeter City without representing them in the League.

Dennis Gratton: Dennis Gratton (born 21 April 1934) is an English former footballer who made 51 appearances in the Football League playing for Sheffield United and Lincoln City.  He played as a centre half.  He also played non-league football for Worksop Town and briefly for Boston United.

Tony Isaacs: Anthony Brian "Tony" Isaacs (born 8 April 1973) is an English former footballer who made 51 appearances in the Football League playing as a midfielder for Darlington.  He also played non-league football for Bishop Auckland.

Mickey Thomas (footballer): Michael Reginald Thomas (born 7 July 1954) is a former footballer who played for Wrexham, Manchester United, Everton, Brighton & Hove Albion, Stoke City, Chelsea, West Bromwich Albion, Derby County, Shrewsbury Town and Leeds United.  As a Welsh international, he made 51 appearances and scored four goals.

Peter Houghton (footballer): A forward, Houghton made his breakthrough into professional football at 23 when Wigan Athletic were elected to The Football League in 1978.  He had joined the Latics a few months earlier from South Liverpool, after an earlier spell with Prescot Town where he won a Mid–Cheshire League championship.  He had the honour of scoring Wigan's final goal as a non–league club against Matlock Town and helped them win the Lancashire Junior Cup against Chorley.  He finished the 1977–78 season with nine goals in 17 league appearances.

Supporting paragraphs: Billy Houghton Watford F.C.
Answer: the Premier League