"What happens if ...?" is a common question asked of experienced players. The short answer would be "Read the rules ", but that wouldn't leave me with much of an article. So:

The questioner usually falls into one of three categories;

First Principle - Chess is a game for people of integrity

It is not uncommon for a section of 20 or more boards to be under the control of a single arbiter in a congress, and this is as true for events such as the British Championships as for a local weekender. Clearly most of what happens goes on unseen by an independent referee/umpire/judge, and this can only happen if the assumption that players will as far as possible act with propriety is correct. There are always a few who see this as an opportunity to gain personal advantage, but after 25 years I can still count on the fingers of one hand those whose behaviour is so far from the reasonable that I would prefer to have nothing to do with them.

Know your laws I - law 6.12b

A player may stop the clocks only in order to seek the arbiter's assistance, for instance when promotion has taken place and the piece required is not available.
By implication

The role of spectators

Spectators have no role. They may not interfere in a game even if invited to do so by the players. Resetting a clock by invitation at a time control is not normally regarded as interference. Note that players count as spectators as far as other games are concerned, though where no arbiter is present certain players may double as arbiters. Non-arbiting roles of captains is a grey area which may be clarified on a competition by competition basis.

Put simply chess is a game for two players, and if they play on through a host of irregularities that is of no concern of spectators.

Know your laws II - Law 13.4

The arbiter can apply one or more of the following penalties:
  1. warning,
  2. increasing the remaining time of the opponent,
  3. reducing the remaining time of the offending player,
  4. declaring the game to be lost,
  5. reducing the points scored in a game by the offending party,
  6. increasing the points scored in a game by the opponent to the maximum available for that game,
  7. expulsion from the event.
This is a general catch all law within section 13, the role of the arbiter. Some of the other rules do specify penalties - I will let you discover these for yourselves - but 13.4 gives the arbiter the power to prevent a player from gaining from any breach. He can apply a penalty whenever there is a breach, including if a player calls them unnecessarily or when a player distracts their opponent. Amongst other things repeated and/or fatuous draw offers are regarded as distractions.

There is no set scale since not only is it not possible to foresee all possible problems, but the time at which they occur can have a bearing on their effect - problems that occur when you are in time trouble are more disconcerting than those that happen when you are comfortably placed on the clock.

No Arbiter Present

Matches are usually played without the presence of an arbiter. Normal practice is for the captains (or sometimes for their nominees) to act as joint arbiters. Given the difficulties that many clubs experience in appointing captains it is clearly desirable that calls for their services as arbiters is kept to a minimum. To this end clubs are encouaged to ensure that their players know and comply with the rules, and that when they inadvertently breach them they acknowledge the fact with good grace and correct things as necessary without making a scene. The "I think that rule is silly and nobody will penalize me so I will ignore it" attitude that some people have towards say, rules about recording moves, is unsatisfactory (at best!).

Joint arbiters means acting together, not that either may act alone. The role is of course one of neutrality rather than as seconder of their players case.

And Finally ....

There is nothing more certain to put people off the game than being picked up by some officious opponent for every minor infraction (and with the changes in the recording law there will be plenty of those to come). The purpose of this article is not to encourage nit-picking, rather it is to reassure players that they do not have to suffer if their opponent displays a blatant disregard for the rules.