According to the 'Family and Personal Life' section of Wikipedia's biography of Ian, he is a fan of the Seattle Mariners Major League baseball team, and quite an avid one at that!
Family and personal life "From 1970 to 1974, Anderson was married to Jennie Franks, a photographer who is credited with writing most of the lyrics to the song Aqualung. Anderson married Shona Learoyd in 1976, described by Rolling Stone magazine as a "beautiful convent-educated daughter of a wealthy wool manufacturer". She had studied ballet for 10 years, though Anderson met her when she was working as a press officer at Jethro Tull's then record-label Chrysalis Records. She later became involved with the band's on-stage special effects.
The couple have lived in a 16th-century redbrick farmhouse on the 500-acre Pophleys estate in Buckinghamshire, England, and on the Isle of Skye in Scotland. They currently live in Wiltshire, England. They have two children: James Duncan Anderson, also a musician; and Gael, who works in the film industry and is married to the actor Andrew Lincoln.
Anderson is a survivor of deep vein thrombosis, and has done several public service announcements to raise awareness of the disease.
Among his interests Anderson lists protecting wild cats, especially those that have been rescued from harsh captivity; cameras, chiefly Leicas; Indian cuisine – he has written a beginner's guide, thus far published only on the Internet.
Anderson describes himself as being "somewhere between Deist and Pantheist" religiously, according to his foreword to the pamphlet for his 2006 St. Brides charity concerts for the homeless.
Anderson has never taken the driving test, though he lists off-road motorcycling among his interests.
Anderson is an avid Seattle Mariners fan." --------------------------------------------------------------
Now, I'm guessing that this is probably joke by an unscrupulous contributor -- I don't see Ian being an 'avid fan' of any sports team -- but you never know!
I live in Seattle (once called "See Tull" by Ian at an early 70s concert here) and even I am not a Mariner's fan. Have attended several of their games but, to use the American idiomatic, they suck. They haven't even made the playoffs for many years. If Ian is a fan, more power to him!