per Official Rules, a batter awarded a base on balls may refuse to advance to first base.
why would a batter do that?
did such a case happen in MLB history?
The obvious case is a batter known to hit well, where the balls have come from a pitcher wanting to avoid the big hit against them.
In particular, this is a good decision
late in the game where the result of a hit is more likely to be unrecoverable
where the batter is especially good at hitting home runs, and the game is very close in score
there are runners on base, particularly if they're on third or a fast runner on second
Combinations of the above scenarios make the decision even more weighted towards staying on the plate to try for the hit.
The only mention the linked rule (9.14) makes of the batter refusing first base is
(c) If a batter awarded a base on balls is called out for refusing to advance to first base, the official scorer shall not credit the base on balls and shall charge a time at bat.
The rule doesn't make clear under what circumstances a batter can be called out: does the umpire simply do so for the batter failing to take the base, or does the opposing team need to take some action?
Rule 5.05(b) provides situations where a runner is "entitled to first base without liability to be put out (provided he advances to and touches first base)". Rule 5.05(b)(1) then specifically mentions that one such situation is when the umpire calls four balls.
The comment on Rule 5.06(b)(4)(I) gives the opposing team the opportunity to execute an appeal play should a batter fail to touch a base to which he was otherwise entitled to. This could apply to a batter failing to take first base after a walk, though it isn't entirely clear.