For such a peripheral and largely undesirable job, the role of 12th man has at times managed to throw cricket's fabled sense of fair play into question. Take Ricky Ponting, so much a traditionalist that he seemed undressed without his baggy green, on the wrong end of modern Test cricket's most (in) famous act of substitute fielding. You may remember it.

By the fourth instalment of the 2005 Ashes, England's habit of allowing their rotating assembly of quicks to enjoy restorative "comfort breaks" had pierced Punter's flesh and was slurping at his boiling blood, where followed an eruption at what he believed to be, frankly, cheating. Where the substitute had hitherto been provided by the host county, some sprightly young buck on a summer contract and very much an afterthought, the sense was that Gary Pratt, a Durham 2nd XI player, was chosen by the ever-scheming Duncan Fletcher with malice aforethought, a weaponised backup carried around the country like a lucky charm, a provocation.

Pratt's swoop-and-shy earned him a visit to 10 Downing Street and an open-top bus ride through London. Other subs have written themselves into folklore - from a 45-year-old Bob Taylor leaving the sponsor's box to keep wicket in a Lord's Test (thanks to New Zealand's amenability) to Bilal Shafayat's dilatory glove-ferrying in Cardiff - yet the 12th man isn't all glory, nor always a particularly easy ride. In many ways it's a highly stressful situation - imagine shelling Virat Kohli off Jimmy Anderson! - if only because of the griping on social media that your "inferiority" should be reflected in your garb: No Three Lions for you, sonny boy, but if you don't catch that crucial, swirling steepler, you'll be for the stocks!

Twelfth man in the club game is an altogether different gig, not least because they rarely come from your own club (if they do, it's old Harry, three sheets to the wind, who only strolled down to walk the dog and get away from the wife for an hour and now finds himself fielding for 43 overs, hiding at slip, exactly where the ball keeps going). No one in their right mind is going to volunteer to be 12th man. Finding an eleventhers is usually hard enough, never mind someone willing to run on towels and gloves and isotonic drinks instead of playing. There are just too many leisure options these days…

For one Twitter interlocutor, Nabi's actions were rationalised by the stakes, by the heavy presence of money. "There's millions of dollars on the line" came the justification

No, usually in the club game if a 12th man is required - and if he's required, this could mean the game is amicable enough to allow it, or meaningful enough that the disadvantage must be compensated - then he or she usually comes, with a certain amount of reluctance, from the opposition, some sheepish interloper hoping he doesn't take a flying catch (although, if he is capable of this, then his team needs a root-and-branch review as to how he was selected for the role), hoping he doesn't "do a Gary Pratt" on his captain - or, depending as to where he's been asked to bat, perhaps hoping he does do a Gary Pratt on his captain.

The whole thing is riven with ethical questions. If an opposition player dislocates a shoulder, what do you do (apart, obviously, from getting the footage on social media)? What about if he goes off feeling poorly? What if some players offer Bartleby's "I would prefer not to"? What if there's too much bad blood? At any rate, in the lower echelons of the recreational game, with the increasing dearth of volunteers, two of the batting side will be umpiring, one scoring, two at the crease and a minimum of three padded up. That doesn't leave many options.

Some of these issues cropped up in an emotive post that appeared on my Facebook feed recently, in which a disgruntled senior pro who recently represented England Over-50s canvassed opinion about a highly unusual scenario from his team's latest game.

They had posted 215 for 6 from their 55 overs, but had lost a man to injury in the process. The opposition obliged with a sub, then another, before a third came on, slowly and unenthusiastically, and was stationed at square leg, where, apparently, he deliberately dropped a catch, "slapping the ball down" and informing his opponents he had no real interest helping them. They asked him to leave the field, playing out the game with ten. The reprieved batsman was on 41 at the time, and finished on 95 not out, carrying his bat as his team hung on for a draw, eight down.

Not a great deal of contextual detail was painted in. (Why did he take the field if he wasn't prepared to try? Was this prompted by some ill feeling over a prior incident?) The immediate response was almost universal in its condemnation. "Name and shame", suggested a couple on the thread. More moderate replies ventured that trial by social media was unfair (the post was removed a day or so later). Others indicated that had it been a member of their club, he would never have played again. "It can't have been a proper cricketer", surmised someone else. "Disgusting", "appalling", "disgrace" they said, with a modicum of surprise that the whole thing didn't end in a brawl. Was this the breaking of a cricketing taboo?

"The spirit of cricket" is a much maligned notion in certain quarters, despite its eloquent advocacy by two of modern cricket's most pugnacious players. Brendon McCullum and Kumar Sangakkara have both expressed the fundamental importance of adhering to a certain moral code that underpins cricket's capacity to elevate its participants beyond a win-at-all-costs ethos.

Take, for instance, Mohammad Nabi's recent shamelessly brassnecked act, failing to own up to lying across the rope as he fielded a ball for Afghanistan in an ODI against Ireland, with Ed Joyce, perhaps a little dopily, being run out in the confusion. Nabi was rightly reprimanded by the ICC, although his many apologists on Twitter could only ask: What law has he broken?

The implicit viewpoint here seems to be that life is about getting away with what you can, that the full burden of ensuring propriety falls on some external "policing" agency. Honesty is for fools! All of which fails to grasp the difference between legal and ethical compunctions, the importance of the latter as a social adhesive and thus the corrosively cynical atmosphere that the "legalistic" standpoint establishes. Applied to politics, you have endemic corruption. Applied to parking your car, you have gridlock. For one Twitter interlocutor, Nabi's actions were rationalised by the stakes, by the heavy presence of money. "There's millions of dollars on the line" came the justification.

That's a whole other can of worms. But what about our loco locum? What about the ethical obligation weighing upon the Saturday afternoon 12th man while helping out the opposition? And might there be contexts in which it is simply too much to ask - last day of the season, promotion and relegation on the line?

An old pal suggested that a sub fielder you provide should never be asked to stand in a catching position. "But where isn't a catching position?" I asked. "In the pavilion". "True, you've never dropped anything in there…"

Scott Oliver tweets here