Question: What year did a speedway club return to a stadium that was built as a football ground?

Context paragraphs:
Rushton Park: Rushton Park (known as Bendigo Bank Stadium under a naming rights agreement) is an Australian rules football ground located in Mandurah, Western Australia.  Having been in use as a football ground since the early 1960s, the ground is currently used as a home ground by three clubs: the Peel Thunder , competing in the West Australian Football League (WAFL), the Mandurah Mustangs, competing in the Peel Football League (PFL), and the Peel Thunderbirds, competing in the West Australian Women's Football League (WAWFL).  Rushton Park is the only regularly-used ground in the WAFL that falls outside the Perth metropolitan area.

Holker Street: Holker Street, also known as the Furness Building Society Stadium for sponsorship purposes, is a sports stadium located in Barrow-in-Furness, Cumbria, England.  Currently and originally used as a football ground, it has also previously been used for speedways races.  In addition, the ground also previously had some leisure centre facilities, including four squash courts which have now been demolished.  Its current owners and tenants for the vast majority of its history are Barrow A.F.C., who have played at the ground since 1909.  Despite having a present capacity of just under 11,000 , some 16,874 people crammed the stadium in January 1954 when Barrow played Swansea Town in the FA Cup third round.

Seedhill Football Ground: The Seedhill Football Ground was a football stadium in Nelson, Lancashire.  It was the home of current North West Counties League Division One side Nelson F.C. from 1905 until 1968.  Nelson later moved to Victoria Park, before the ground was demolished in 1980 to make way for the M65 motorway.  The ground was situated near to the Seedhill Cricket Ground, currently the home of Lancashire League cricket team Nelson Cricket Club, and the perimeter red brick wall is still visible on the Cricket Ground and Victoria Park sides.  In April 2009, the football club announced plans to return to the Seedhill site.

European Speedway Club Champions' Cup: The European Speedway Club Champions' Cup is an annual speedway event held each year in different clubs organized by the European Motorcycle Union (UEM) since 1998.

Pride Park Stadium: Pride Park Stadium is an all-seater football stadium in Derby, England, that is the home ground of English Football League club Derby County.  With a capacity of 33,597, it is the 16th-largest football ground in England and the 20th-largest stadium in the United Kingdom.  Located on Pride Park, a business park on the outskirts of Derby city centre, the stadium was built as part of the commercial redevelopment of the area in the 1990s.  Derby County have played at the ground since it opened in 1997 as a replacement for their former home, the Baseball Ground.  Due to sponsorship, the venue was officially known as the iPro Stadium between 2013 and 2016.

Barrow Bombers: The Barrow Bombers were a Speedway team promoted in Barrow-in-Furness.  Speedway had been promoted at a number of venues.  In 1930 a number of meetings were held at Holker Street, the home of Barrow A.F.C. the towns football club.  Racing moved to Little Park, Roose in 1931 but crowd levels were insufficient.  Speedway returned to Barrow in 1972 back at Holker Street when the former Romford Bombers promotion who started the season at the West Ham Stadium in London moved the team north.

Motordrome (Melbourne): The Motordrome, also known as the Olympic Park Speedway, the Melbourne Speedway or the Victorian Speedway, was a former speedway and Australian rules football ground located on the site of Olympic Park in Melbourne, Victoria.  The ground was primarily a speedway track, but also hosted football matches.

Workington Comets: Workington Comets is a speedway club based in Workington, Cumbria.  Their track is at Derwent Park Stadium, which they share with Workington Town Rugby League Football Club.

Leederville Oval: Leederville Oval (known as Medibank Stadium under a naming rights agreement between 2006 and 2016) is an Australian rules football ground located in Leederville, a suburb of Perth, Western Australia.  The ground is currently used as a home ground by two clubs: the East Perth Football Club and the Subiaco Football Club, both competing in the West Australian Football League (WAFL).  The ground was previously home to the West Perth Football Club from 1915 to 1993, before the club moved to Arena Joondalup, its current home ground.  The ground is serviced by the Joondalup railway line, with the nearest stop being the Leederville station.

Griffin Park: Griffin Park is a football ground in Brentford, situated in the London Borough of Hounslow, Greater London.  It has been the home ground of Championship side Brentford since it was built in 1904.  The ground is situated in a predominantly residential area and is known for being the only English league football ground to have a pub on each corner.  The ground gets its name from the griffin, featured in the logo of Fuller's Brewery, which at one point owned the orchard on which the stadium was built.

Supporting paragraphs: Barrow Bombers Holker Street
Answer: 1972