I wrote rules for pikes and wanted to try them out, so I came up with this one.
One side has a pike block. I used a three-rank deep block five men wide (15 figures) of guys in decent armour (or else shooting them would be too easy). It also has a small escorting force, with a leader, five decent swordsmen, and a scattering (perhaps fifteen) of poor skirmishing troops. It has to get to the other side of the table.
The opposing side has a shieldwall of decent spearmen (about seven of them) which it places on the other side of the table directly in front of the pike block's objective. This shieldwall will not crumble the instant the pikes hit it, but the odds are that it will be pushed back after a few rounds of combat. The opposing force also has fifteen or so good troops, including a few archers, and troops useful in melee. If it can strip the pike block of its escort, then the pike block itself should be easy meat.
There are two versions of this scenario.
Version One: There are three exits of the far side end of the table. One is in the centre, and this is where the pikes will go. It is the entrance to a narrow gorge, defended by the opposing spearmen. Near the corners, either side, are two more exits, through which allies of the pike block might flee. The pike block side wins if half its troops exit the far end of the board. Many could do this just by rushing to the corners, but that would leave the pike block very exposed. If you play this version, the pike block should make up almost but not quite half the numbers of the whole side, so that abandoning the pike block to its fate is a strategy that might just work, but only if the rest of the force suffers very few casualties.
Coming up for a rationale for this will depend on your setting. In a fantasy world, you could say that the pike-using side is returning to its own territory, and the pikes are large orcs who must go through the Gorge of Glath, while the escorting goblins and lesser creatures could scuttle down into the entrances of the Chasms of Quarg. A non-fantasy setting might be where the troops are following orders to play their part in a larger action, and are trying to fight their way back into their town. The pikes have been ordered to advance along the road and clear a path to one of the main gates, while the commander of the escorting force has half a mind to save his force by getting his men through a couple of little sally ports in the town walls. The townsfolk will let them in if they can get to the sally ports (small entrances/exits in fortifications), and it would be suicide for any forces to follow them inside.
Version Two: There is an objective on one edge of the table, which is small and immobile. If any of the pike-using side can get to this objective, then it has won. I played this game in 25mm scale across a table four foot across and this was plenty of space. The terrain involved a major obstacle directly in front of the pike block, which started in the centre of one side. The pike block therefore started by having either to cross the obstacle and become broken up by it, and dangerously vulnerable, or else manoeuvre around the obstacle which is not easy for pikes to do. The terrain left a clear path for the pikes to the objective, and involved many fences and woods and such-like either side, for defenders to hide archers behind, and to rush out from and harass the pike block or its escort.
The two obvious ways to win for the pike-player are to smash through to the objective with the pikes, or to get one lightly equipped fighter to slip away from the fight, while everyone else is busy dealing with the pikes, and run round the back to the objective. Thus the defender has two worries: the pike block, and the stragglers around it.
When I played this one, it was a fantasy setting and the objective was a huge grille set in the ground, held shut with a bolt. One fighter could throw the bolt and release some ghastly monster held captive underground and by this win the game. The objective could instead be a powder magazine that could be detonated by one trooper, or a holy relic that could be desecrated/rescued.
Keeping the pike block secure should be a problem for the attacker, and the attacker should not be able to afford to lose the block. If the block breaks and runs, the morale effect of this should be very significant, and the attacker's force should withdraw if it suffers just a few more losses than this. If your rules do not make a pike block vulnerable if attacked from all sides, then you will have to invent some rules to make this true. If your rules do not take morale into account, then you should simply decide on a number of casualties that the attacker can afford to take, above which his men will withdraw.
The game ends when the objective is reached or when the attacker's forces withdraw. Once broken, the pikes will not reform. You could have the defender fight to the last (so make the objective very important), or if you prefer rule that the defender too might run for it after so many losses.