Assists are not awarded for winning penalties or being involved in own-goals.
Assists are awarded for shots that hit the woodwork and rebound to a teammate who has scored.
Free-kick goals are scored following a passage of play that originated from an indirect free-kick.
Direct free-kick goals are scored directly from the free-kick taker without any other player involvement.
Throw in goals are scored from a phase of play that originated from a throw-in.
Penalty rebounds are goals scored from a follow up shot after the initial penalty was not converted.
Fast break goals are scored after a defensive phase of play has quickly turned into a counter attack by winning the ball in the defensive half of the pitch. 

Assists made after the 2012/13 season are recognised by Opta. All assists pre 2012/13 follow the same conditions and have been thoroughly researched
through match clips and cross-referenced with Leeds United, BBC and Sky Sports match reports.