Under the Mat: Inside Wrestling's Greatest Family is a book co-written by Diana Hart (daughter of Stu and Helen Hart, ex-wife of Davey Boy Smith and mother of Harry Smith) and journalist Kirstie McLellan.

[5][6] The writing of the book was at least partially motivated by the death of her younger brother Owen Hart.

She remembers her father training some of the WWF's and WCW's biggest names in her family's basement gym, the famous Dungeon, and recounts their tales to stardom.

It has been criticised for its factual errors, grammatical mistakes, spelling issues and unstructured content.

According to employees of the Toronto-based law firm Cassels Brock & Blackwell LLP, a preliminary review of the book identified dozens of significant factual errors.

[13][14] People like Dynamite Kid, Ben Bassarab, Davey Boy Smith and Jim Neidhart are in the book accused of several occasions of criminal activity.

[18] Her brother Bret is a vocal critic of the book and has said that it is a very disturbing read and called it pornographic.

[24][25] She stated that the book was “filled with distortions, misstatements and unjustified slurs that attempt to destroy the reputation of my family and me, and undermine the memory of Owen.”[26] Diana defended herself in an interview for the National Post and stated that she stood by what she has written, insinuating that Martha was a rich bully who was trying to use her money to suppress her recounts.

[28] Long-time wrestling announcer and Stampede alumni Ed Whalen also discredited the book, referring to it as a "fairy tale" and considered joining Martha Hart in the lawsuit.

[31] Tom Billington, professionally known as The Dynamite Kid, admitted to some of the criminal actions he was accused of in the book.