I think you are always allowed to throw the game and still be a sporting player. I will illustrate with a situation where it looks like someone can get a draw, but he won’t get it if throwing isn’t allowed, but will get it if it is:
Suppose you have the situation: It is the Spring turn) Player A threatening to solo, players B and C holding him off. It may well be (with an appropriate position), that the 2 players each have two strategies: work with A or with the other of B/C. Let’s (suggestively) call these “Cooperate” and “Defect” for cooperating with the other of B/C or defecting against him:
Both cooperate and the game will be drawn
Both defect and the game is immediately won by player A (as in, he can force a win in Autumn
One cooperate and one defect, and the game moves on to the Autumn turn:
(Without loss of generality, suppose B defected against C)
B can work with A or C; C can work with B or throw the game. The payoff matrix is:
B strategy.....work with A........work with C
C strategy =======================
..work B....¦¦....A-B 2-way.............3-way......
..throw.....¦¦.........A solo................A solo.....
Here C has a chance of getting a draw, (which means he should take it). But at the same rate, player B is best off working with player A, that strategy is dominant. Nevertheless, there is still a non-zero possibility that player B will choose to work with C, so it is demanded that he take it.
This leads to the (common) assumption that in the Spring turn, the payoff matrix is basically 2-way if one player defects and the other player co-operates (we have a prisoners dilemma, in fact)
If we allow people to throw games in this situation however, then if a player defects and the other cooperates, there is a non-zero chance that player A just wins. This actually changes the decisions being made before the game is actually thrown.
In light of this, I find it odd that people complain that someone pre-committed to throw the game, and then actually did. The point in /actually/ precommitting was to make it more believable a threat, and in so doing, increase the chance of getting involved in the draw. It is the mistake of the other guy not to believe the threat was real.
Sometimes Timeless Decision Theories outperform Causal Decision Theory, so people, innately (via a sense of honour, or justice etc.) or intentionally use it.