At the time the poison pill is setup no shareholder has the threshold. If you buy more shares and cross the threshold you did so in full knowledge of the effect

At the time the poison pill is setup no shareholder has the threshold. If you buy more shares and cross the threshold you did so in full knowledge of the effect. If the pill were activated and you were diluted out you could sue over the economic harm e.g. that they effectively stole half your position-- and you'd quite possible be reimbursed for the dilution. But you'd be more or less back where you started, minus the mountain paid to lawyers and still without ownership of the company. Keep in mind, these poison pills aren't really intended to prevent acquisition. They're intended to prevent an inequitable acquisition via takeover where the existing shareholders might have to sue to get a fair treatment. E.g. elon getting enough control that he can pick the board (which takes less than 51% of the shares due to voting power effects)... then the elon controlled board agrees to sell the rest of the company for a less equitable price but not so outrageous that the other shareholders would have an easy time suing over it. > What if there was some minority shareholder that the other owners disliked for some reason, could they force them out too? Or this power is restricted to particular circumstances? Diluting out small share holders happens with some regularity in smaller companies. They could sue over it-- but it usually happens when there isn't a lot of value in the company itself and if they failed to push out an old shareholder the company wouldn't continue. So the party being diluted can only really choose between letting it happen or fighting it and getting their fair share of nothing minus legal expenses.