But if you read the Moldvay Basic rulebook you will not see any such rule, because Moldvay Basic is not a board game.
Here is the basic rule for permissible player-side move (ie action declarations) in Moldvay Basic (pp B2, B3, B4, B60):
The D&D game has neither losers nor winners, it has only gamers who relish exercising their imagination. The players and the DM share in creating adventures in fantastic lands . . .
This game . . . does not use a playing board or actual playing pieces. All that is needed to play are these rules, the dice included in this set, pencil and paper, graph paper, and imagination. . . .
At the start of the game, the players enter the dungeon and the DM describes what the characters can see. . . the players should select one lay to speak for the entire group . . . That player is named the caller. When unusual situations occur, each player may want to say exactly what his or her character is doing. . . .
"That's not in the rules!" The players will often surprise the DM by doing the unexpected. . . . All DMs learn how to handle both new ideas an unusual actions quickly and with imagination. . . . One quick way for a DM to decide whether a solution will work is by imagining the situation, and then choosing percentage chances for different possibilities.
What characterises D&D, and other games in the same family of games (generally known as RPGs or "TT" RPGs), is that the permissible moves are not defined in advance by a set of rules or formulas or mechanics for defining and transforming the "gamestate".