THEY HURRIEDLY dug a circular trench with crude shovels.And the soil they wrenched from the earth, they piled and packed in mounds, building an earthen wall around the inside of the dyche. They poured water in the dyche, then laid a bridge over the shallow moat and posted a gatekeeper at one end of the bridge. The gatekeeper checked the human traffic crossing the bridge,and collected donations at the entry to the arena.

They raised a small stadium, in this way, on the soft Lincolnshire ground in 1425. And where the ground was too hard to shovel, they raised fences and stronglye barryd the circle inside. They were medieval managers. Their business was staging what the English called morality plays.

These miniature stadiums, or "Rounds," were not unlike the monstrous steel-and-concrete sports arenas that dot the plains, marshlands and cities of this country.In fact, the small moated stadium at Lincolnshire, raised to stage "The Castle of Perseverance," somewhat resembled the big parks for our great national pastime, baseball.

The moat and earthen embankment were, like the circular, tall walls on Astrodomes, barricades to gatecrashers. Pedestrians followed the moat or fence to an authorized entrance, to a hole in the circular barricade. Passing through the gate, the medieval spectator was likely to find himself timidly staring down the stave of a styteler. A styteler was a brawny medieval usher armed with a solid wooden staff, or stave. Like ball-park ushers, the styteler grudgingly sort of pointed to no particular area and barked, "Move on!" Bobbing the blunt end of his heavy stave in front of a pale medieval nose, he grunted again, "Move on!" - putting an abrupt stop to any more questions about seating.

Actually, the bobbing, blunt stave was only a precautionary tactic, a warning to impetuous pranksters. The brawny styteler was a primitively armed stadium policeman. His job was to indiscriminately bruise bones, crush teeth and skulls whenever overly zealous spectators interfered with the play. It was not unlikely that the rowdy medieval fan might leap onto the field for an autograph, or throw wooden bowls and other Middle Ages debris at villainous characters. Pranksters are pranksters, in any age. Any head, medieval or modern, that has been brusied by a billy-club in the fist of a stadium guard knows painfully well what stytelers and staves are.

Medieval spectators could either sit in the grandstand or stand in elevated booths. The medieval grandstand was not too terribly different than a modern grandstand. It, too, was awkwardly terraced into the inside wall of the stadium, and was by no means any more comfortable than the stiff bleachers circling the outfield walls. If medieval producers bothered at all to terrace the earthen embankment for seats, they terraced the dirt with stones. They built grandstands out of rocks. And there they sat, the bottom-weary spectators, perhaps for hours, squirming on their stone seats, and fearful that if any one of them should stand at the wrong moment, some stave-happy styteler might unload a healty-clout on their skulls.

Fortunately, there was an alternative to the stone-seat grandstand. Erected along the top of the earthen wall were a number of small, curtained booths, akin to tree houses, which could be reached either by stairs built into the dirt mound, or by ladders. While there were no stools or chairs in these simple booths, and most spectators stood or leaned against the wooden columns, some fans sat on the floor, dangling their legs over the sides, teasingly over the heads of the stytelers. Although the booths were no guarantee against the clouts and proddings of the stytelers, they did, at least, make the spectator more difficult to reach.

It has been suggested that the elevated stave-proof booths were actually first-class accommodations, and not open to commoners. Occupants of these booths did enjoy an aerial view of the play. Canopies shielded them from the elements. And, of course, primping up there in the air, they could be seen. It may very well have been that these lofty berths were posh boxes for the upper crust and the high culture. Perhaps these simple boxes were the Sky Suites of the Middle Ages, with a view looking down on the grandstand.

In a pavillion beyond the Round, the players would change dress and metamorphose into outlandish, allegorical characters, like Good Deeds and Old Vice. Costumed and masked, the performers then inched their way along the top of the earthen mound, slipping unnoticed behind the spectators, climbing quietly through the back curtain into one of the boxes. There they mingled with the upper crust, and waited for a cue. On cue, Good Deeds and Old Vice flamboyantly paraded from the booth to the field.

Each character had a home booth. These were variously called domus, sedes, tentus. They were, in a sense, bases laid out around the Place like bases in a ball park, like the points on a compass. Players scrambled and strutted from domus base to sedes base to tentus base along base lines kept clear by the brawny stytelers. And all the play whirled about one solitary, central and rather obvious raised figure. In the medieval Round at Lincolnshire, it was castle, and the conflict took place between the vices, who wanted to topple the castle, and the virtues, who, of course, wanted to protect the castle.

All this, the parade of characters and the conflict between good and evil, should seem at least vaguely familiar, particularly to fans who find themselves gluded to the tube every Saturday afternoon watching baseball. A baseball team is, after all, a parade of medieval characters, a cast of virtues and vices. The players change dress and metamorphose in a pavillion we know as the locker room. Uniformed and capped, some masked, the players slip unnoticed by the spectators through the back door of a box or booth we call a dugout. On cue, they enter with a flamboyant charge, scrambling and strutting from home base to first base and so on, all a matter of toppling and protecting a solitary, central and rather obvious raised figure: the pitcher on his mound castle.

And so, perhaps, we discover a new theatrical basis for this popular sport, an allegorical contest between a Home Team and a Visiting Team, between Good Deeds and Old Vice.