In facing up to this question himself, Nelson has gone some of the way to answering it with the publication of Left Foot Forward (Headline), his diary of the 1994-95 season, in which, with vividness and honesty, he portrays life as an ageing pro in an industry which looks very different from the inside of the changing-room than it does from a nice seat behind the goal. One of the surprise hits of 1995's crop of sporting literature, Left Foot Forward is on the short list of six for the William Hill Sports Book of the Year Award, the winner of which will be announced on Wednesday.
At a time when television is awash with football nostalgia masquerading as social history, and bookshops groan under the weight of fan memoirs that would all like to have been Nick Hornby's Fever Pitch, there is something very welcome about the authentic way Nelson's book takes one into the world of the contemporary footballer. There is none of the blandness of the standard-issue ghosted autobiography, none of the self-indulgence of those who seek to derive credibility from their association with the lower end of the professional game.
Which is not to say that in detailing the day-to-day existence of your average footballer - the slog of training, the tedium of long- distance coach travel, the joy of scoring a goal, the fear of being dropped - Nelson is breaking entirely new ground. Twenty years ago, in Only A Game?, the Irish international Eamon Dunphy brought a similar candour and literacy to bear on life at Millwall. Perhaps there is something in the south London air that brings out the author in a player: Dunphy's classic chronicle of the first four months of the 1973-74 season ends with his transfer to Charlton.
Mention Only A Game? to Nelson and his response bears the merest trace of irritation. "I was totally unaware of Eamon's book until people started writing about it in reviews," he said when I met him at Dillons bookshop in Plymouth, where, as a former Argyle player, he had gone to do a signing session. "I'm sure it's very good but when I heard about it I didn't want to read it. As far as I was aware I was writing from an unadulterated source."
A generation on, Nelson need hardly worry that the impact of Left Foot Forward will be lessened by anything published before. He has still produced a rarity: a book by a practising sportsman that seems to tell it like it really is, intelligently and engagingly. Of the 41 other books short- listed since the William Hill award began in 1989, only one belongs to this genre, A Rough Ride by the cyclist Paul Kimmage, which was good enough to win in 1992.
As with Kimmage's book, a constant theme in Nelson's is the insecurity of the professional sportsman. What if I have a bad game tomorrow? Are we signing somebody who might take my place? Am I going to be offered a new contract? Nelson thinks footballers everywhere will be able to identify with it. "What I am writing about at Charlton is being replicated throughout the game."
Fans, Nelson hopes, will come away from the book with an understanding not just of the player, but of the whole man - with, in his case, a wife, two children, a mortgage, and a car that has a tendency to break down on the way to matches. "I was very anxious to try to avoid sounding like a whinger, because of course we're very lucky in what we're doing," Nelson said. "People say what a great job, and it is. But there are sides that are not so great, and it seems almost part of the spectator's role not to know about them."
That Nelson is the sort of player most people outside Charlton Athletic Supporters' Club don't know about is precisely what makes the book work. It couldn't have been written by a star. Or rather it could, but it wouldn't. Nelson's career makes him ideally qualified to write about "a year in the life of a journeyman footballer" - the book's secondary title.
Born and brought up in Essex, Nelson turned down the chance to go to Loughborough University to play for Southend United. After four seasons there, he went to Swindon, then Plymouth and then Brighton before joining Charlton in 1991. "I've always had to work very hard to get as far as I have," he said. Nelson's awareness that there are other players with much more innate talent than he has is the source of much of the book's self-deprecating humour.
Nelson had kept a diary for a couple of seasons before the seeds of Left Foot Forward were sown when he got chatting to a Charlton supporter, Anthony Fowles, on New Year's Day 1994, after a match at Nottingham Forest. Fowles, an author, suggested they do a book together.
"I wasn't just going to talk into a tape-recorder," Nelson said. "I wrote up each day and sent stuff off to Anthony and then he would bring his skill to it. But if there was anything in there that wasn't Garry Nelson then that came out. The great thing is a lot of family and friends have read it and have told me it is exactly how I sound."
Keeping the book a secret from everyone at Charlton, Nelson did not look for a publisher until he had written about 100 pages. There was a polite rejection from one - "She said there was a bit too much of me in it, which I thought a bit strange considering it was a diary" - before Headline got hold of it.
Nelson was dismayed when they asked him to cut it from its original 160,000 words to 90,000, although it has ended up at 105,000. "I still think it's been cut a bit too much in places," he grumbled. Published in September, Left Foot Forward is now into its third print run and has sold more than 6,000 copies in hardback. "Charlton weren't quite sure what to make of it, but they're pleased now because it's been a best-seller in the club shop."
What about Nelson's team-mates? How have they taken to being put between hard covers by one of their own? "One or two are a bit disappointed because they've had to go out and buy a dictionary," Nelson said. There's plenty of sardonic humour like that in Left Foot Forward, even though Nelson has been loyal to his fellow pros, the much-maligned and misunderstood people with whom his heart lies. For further insights we must await the football novel Nelson is working on. "You can say more with fiction."
The short list
The Far Corner Harry Pearson (Little Brown, pounds 5.99). Matches in the North-east in 1993-94 provide the basis for Pearson's personal celebration of the region's footballing character.
Out of Bounds Lauren St John (Partridge Press, pounds 16.99). Starting with the Ryder Cup in 1993 and ending with the Volvo Masters in Spain at the end of the following year, one of golf's few women reporters examines the men's tour through a mixture of personal reflection and hard-hitting analysis.
A Good Walk Spoilt John Feinstein (Little Brown, pounds 17.99). Similar territory to that in Out of Bounds is explored by the American famed for the insights he brought to college basketball in Season on the Brink and tennis in Hard Courts. Now the American golf circuit comes under the microscope.
Bull - the Biography Howard Wright (Timeform, pounds 18.95). Wright makes extensive use of the writings of Phil Bull to bring to life the story of the man who changed the face of racing when he created Timeform, the numerical system by which horses are rated.
The Prizefighters Arlene Schulman (Virgin, pounds 14.99). American photojournalist provides both words and moody black and white pictures in a heartfelt look at boxing over the last 10 years.
Left Foot Forward Garry Nelson (Headline, pounds 12.99). Nelson speaks for the majority of professional footballers with his account of life at Charlton Athletic in the 1994-95 season.