Question: Who is the athletic director of the university that used to have Barry Switzer as a head coach?

Context paragraphs:
Oklahoma Sooners: The Oklahoma Sooners are the athletic teams that represent the University of Oklahoma, located in Norman.  The 19 men's and women's varsity teams are called the "Sooners", a reference to a nickname given to the early participants in the Land Rush of 1889, which initially opened the Unassigned Lands in the future state of Oklahoma to non-native settlement.  The university's athletic teams compete in the National Collegiate Athletic Association (NCAA)'s Division I in the Big 12 Conference.  The university's current athletic director is Joe Castiglione.

1973 Oklahoma Sooners football team: The 1973 Oklahoma Sooners football team represented the University of Oklahoma in the 1973 NCAA Division I football season.  Oklahoma participated as members of the Big Eight Conference and played its home games in Gaylord Family Oklahoma Memorial Stadium where it has played its home games since 1923.  The team posted a 10–0–1 overall record and a 7–0 conference record to earn the Conference outright title under first-year head coach Barry Switzer.  This would be the first of eight consecutive Big Eight Conference championships for the Sooners with Switzer as head coach.

Barry Switzer Center: The Barry Switzer Center, on the University of Oklahoma campus in Norman, Oklahoma, houses football offices, the football locker room, equipment room, the Siegfried Strength and Conditioning Complex, the Freede Sports Medicine Facility and the Touchdown Club Legends Lobby.  The Center is located at the south end of the Gaylord Family Oklahoma Memorial Stadium.  The Barry Switzer Center, dedicated on April 24, 1999, was named after OU’s all-time winningest head football coach.  During Summer 2015 the Switzer Center was demolished as part of the expansion of Gaylord Family Oklahoma Memorial Stadium.  In Barry Switzer’s 16 seasons as the Oklahoma Sooners head football coach, the team won three national championships, 12 Big Eight Conference championships and eight bowl games in 13 appearances.

1978 Oklahoma Sooners football team: The 1978 Oklahoma Sooners football team represented the University of Oklahoma in the college football 1978 NCAA Division I-A season.  Oklahoma Sooners football participated in the former Big Eight Conference at that time and played its home games in Oklahoma Memorial Stadium where it has played its home games since 1923.  The team posted an 11–1 overall record and a 6–1 conference record to earn a share of the conference title under head coach Barry Switzer.  This was Switzer's sixth conference title in six seasons since taking the helm in 1973.

1979 Oklahoma Sooners football team: The 1979 Oklahoma Sooners football team represented the University of Oklahoma in the college football 1979 NCAA Division I-A season.  Oklahoma Sooners football participated in the former Big Eight Conference at that time and played its home games in Gaylord Family Oklahoma Memorial Stadium where it has played its home games since 1923.  The team posted an 11–1 overall record and a 7–0 conference record to earn the Conference title outright under head coach Barry Switzer who took the helm in 1973.  This was Switzer's seventh conference title and fourth undefeated conference record in seven seasons.

1977 Oklahoma Sooners football team: The 1977 Oklahoma Sooners football team represented the University of Oklahoma in the 1977 NCAA Division I football season.  Oklahoma was a member of the Big Eight Conference and played its home games in Oklahoma Memorial Stadium, where it has played its home games since 1923.  The team posted a 10–2 overall record and a 7–0 conference record to earn the Conference title under head coach Barry Switzer who took the helm in 1973.  This was Switzer's fifth conference title and third undefeated conference record in five seasons.

1994 Dallas Cowboys season: The 1994 Dallas Cowboys season would mark their 35th in the NFL.  Following their second consecutive Super Bowl title, the Cowboys would see a multitude of changes.  In March, months of frustration finally reached its climax as team owner Jerry Jones and head coach Jimmy Johnson held a press conference and announced Johnson's resignation.  Jones would later hire former Oklahoma Sooners head coach and personal friend Barry Switzer to be the third head coach in franchise history.  After a continue run of dominance in the regular season and finishing with a record of 12–4, the Cowboys fell short of a record third straight Super Bowl title with a loss to the San Francisco 49ers in the NFC Championship game.  The 1994 Cowboys draft yielded only one notable addition to the team, offensive guard Larry Allen and veteran linebacker Ken Norton Jr. left the team to sign with San Francisco.

1984 Oklahoma Sooners football team: The 1984 Oklahoma Sooners football team represented the University of Oklahoma in the college football 1984 NCAA Division I-A season.  Oklahoma Sooners football participated in the former Big Eight Conference at that time and played its home games in Gaylord Family Oklahoma Memorial Stadium where it has played its home games since 1923.  The team posted a 9–2–1 overall record and a 6–1 conference record to earn a share of the Conference title under head coach Barry Switzer who took the helm in 1973.  This was Switzer's ninth conference title in twelve seasons.

1976 Oklahoma Sooners football team: The 1976 Oklahoma Sooners football team represented the University of Oklahoma in the 1976 NCAA Division I football season.  Oklahoma was a member of the Big Eight Conference and played its home games in Oklahoma Memorial Stadium, where it has played its home games since 1923.  The team posted a 9–2–1 overall record and a 5–2–0 conference record to earn a share of the Conference title under head coach Barry Switzer who took the helm in 1973.  This was Switzer's fourth conference title in four seasons.

List of Oklahoma Sooners head football coaches: The Oklahoma Sooners football program is a college football team that represents the University of Oklahoma.  The team has had 22 head coaches since organized football began in 1895.  The Sooners have played in more than 1,200 games in its 121 seasons.  In those seasons, eight coaches have led the Sooners to postseason bowl games: Tom Stidham, Jim Tatum, Bud Wilkinson, Gomer Jones, Chuck Fairbanks, Barry Switzer, Gary Gibbs and Bob Stoops.  Eight coaches have won conference championships with the Sooners: Bennie Owen, Stidham, Dewey Luster, Tatum, Wilkinson, Fairbanks, Switzer and Stoops.  Wilkinson, Switzer and Stoops have also won national championships with the Sooners.  Stoops is the all-time leader in games coached and won, Owen is the all-time leader in years coached, while Switzer is the all-time leader in winning percentage.  John Harts is, in terms of winning percentage, the worst coach the Sooners have had as he lost the only game he coached.  John Blake has the lowest winning percentage of those who have coached more than one game with .353 in his 34 games.

Supporting paragraphs: 1994 Dallas Cowboys season Oklahoma Sooners
Answer: Joe Castiglione