A hard tackling defender, he appeared sporadically for the team in the Southern Football League before his spell at the club was interrupted by the outbreak of the First World War.

In 1926, he replaced the departing Jimmy Blair as club captain, leading the team to success in the 1927 FA Cup Final later in the season, in which they defeated Arsenal 1–0.

[3] His father was a stonemason in the city, working long hours to be able to afford employing Elizabeth Maler, a live-in nanny, to help his wife care for their children.

[8][9] Keenor's former teacher Riden invited him to attend a trial at Cardiff City in 1912 after spotting him playing local amateur football for Cardiff-based side Roath Wednesday.

A loss to Camerton during a Western League fixture left a lasting impression on him after an over-confident Cardiff side suffered an upset, losing 3–1 in a match they were widely expected to win.

[15] The presence of Billy Hardy, Patrick Cassidy and Kidder Harvey, who became known as the "holy three" by fans, restricted his first-team opportunities as the trio ensured the club won promotion to the First Division of the Southern Football League after conceding just 15 goals during the campaign.

[19] During the season, Cardiff came under pressure from local newspapers, most notably the Western Mail, for the club's perceived lack of contributions to the war effort.

[20] The Western Mail printed numerous scathing comments focused on association football clubs and even refused to report on Cardiff's matches for a time.

He eventually enlisted in February 1915, along with teammate Jack Stephenson, trainer George Latham, who had previous military experience having served in the Second Boer War, and two of the club's directors.

Led by former England international Frank Buckley, the regiment had been founded by William Joynson-Hicks, 1st Viscount Brentford, in December 1914 in the hope of attracting footballers and fans into enlisting in the armed forces.

With travel restrictions placed on train services, and local men enlisting en masse, Cardiff's income from attendances dwindled.

Cardiff City organised regular collections at their wartime fixtures during this period to send parcels to Keenor and Jack Stephenson containing letters from fans and home comforts.

The Middlesex Battalion claimed the Divisional Football Cup with relative ease, defeating a team from the 34th Brigade 11–0 in the final on 11 April 1916; each player received a winners' medal made of bronze.

[32]During the battle, Keenor was badly wounded when a piece of artillery shrapnel struck his left leg above the knee on 28 July,[22] leaving him unable to walk.

An unknown soldier saw him attempting to crawl away from the incoming fire and managed to help him back to the nearby medical facilities where army doctors were able to tend to his injury.

They were subsequently promoted to the top tier of English football and reached the semi-final of the FA Cup, losing to fellow Second Division side Wolverhampton Wanderers in a replay.

As the teams left the pitch at the end of the first-half, a furious Keenor, upset at the nature of some tackles he had received, yelled at the Prague players, "If I get anymore kicks on the shin I shall be chopping someone off at the knee".

[49][50] His request was approved by board members Walter Riden and Syd Nicholls and negotiations over a proposed move to Severnside rivals Bristol Rovers were opened.

[57] One newspaper published a caricature the following day, describing him as "the most important man in Wales" with an image depicting Keenor knocking former Prime Minister David Lloyd George off a pedestal.

[59] An ageing Keenor became a target of frustrated fans as Cardiff suffered financial difficulties that saw the majority of the team's star names sold in a bid to raise funds.

[65] Although his advancing years had lessened his abilities, Keenor became a huge draw for Crewe, and if he was unable to play due to injury, the club would withhold the information before the match in fear of affecting attendance figures.

In a match against Scotland in 1929, with Wales unable to call up a replacement, Keenor had to play with strapping to protect his injured neck and was advised by a doctor to avoid heading the ball during the game.

In October 1930, for a fixture in Glasgow against Scotland, a heavily depleted Welsh side who were unable to call up many of their star players as Football League clubs refused to release them for international duty became known as 'Keenor and the 10 unknowns'.

The Welsh featured just seven players from Football League sides, with only Keenor and Cardiff teammates Len Evans and Walter Robbins playing in the top two divisions.

[53] Charlie Buchan, captain of the opposing Arsenal side in the 1927 FA Cup final, described Keenor as having "a store of energy (that) seemed inexhaustible in defending his goal".

[13] In his biography of Keenor, James Leighton stated "he ran tirelessly for the cause and would frequently put his body on the line ... His endeavours could only inspire his teammates to reach a higher standard of play".

[13] Martin Johnes of Swansea University described Keenor as "the quintessential 'British' player: physical, committed and determined, making up in strength for what he lacked in skill.

There he and his wife ran a corner shop and raised chickens to be sold at Christmas time,[88] alongside his player-manager role with Tunbridge Wells Rangers.

[90] After the end of the Second World War, Keenor worked as a builder's labourer for several years, waking up in the early hours each morning to catch a lift in a newspaper delivery van before walking the remaining five miles to the site.

[94] His son Graham, who had joined Cardiff City as a youth player but never appeared for the first team, served as club secretary following the resignation of Trevor Morris between 1959 and 1972.