It is fairly easy for a top executive to reduce the price of his/her company's stock – due to information asymmetry. The executive can accelerate accounting of expected expenses, delay accounting of expected revenue, engage in off balance sheet transactions to make the company's profitability appear temporarily poorer, or simply promote and report severely conservative (e.g. pessimistic) estimates of future earnings. Such seemingly adverse earnings news will be likely to (at least temporarily) reduce share price. (This is again due to information asymmetries since it is more common for top executives to do everything they can to window dress their company's earnings forecasts). There are typically very few legal risks to being 'too conservative' in one's accounting and earnings estimates.
A reduced share price makes a company an easier takeover target. When the company gets bought out (or taken private) – at a dramatically lower price – the takeover artist gains a windfall from the former top executive's actions to surreptitiously reduce share price. This can represent tens of billions of dollars (questionably) transferred from previous shareholders to the takeover artist. The former top executive is then rewarded with a golden handshake for presiding over the firesale that can sometimes be in the hundreds of millions of dollars for one or two years of work. (This is nevertheless an excellent bargain for the takeover artist, who will tend to benefit from developing a reputation of being very generous to parting top executives.)
Similar issues occur when a publicly held asset or non-profit organization undergoes privatization. Top executives often reap tremendous monetary benefits when a government-owned or non-profit entity is sold to private hands. Just as in the example above, they can facilitate this process by making the entity appear to be in financial crisis