I always thought that "to knock down" meant "to make somebody fall by a blow", but I've checked this in the dictionary.com and haven't found such a meaning. Only:

knock
down, a. to sell at auction by a blow of the hammer or to a bidder.

b. to take apart or disassemble, as for facility in handling, storing, shipping, etc.

c. Slang. to receive, as a salary or a scholastic grade; earn: He knocks down 30 grand a year.

d. Informal. to lower the price of; reduce: to knock down end-of-season leftovers.

e. Slang. to embezzle or steal (money).

f. to cause (a sailing vessel) to heel, as by a gust of wind, to such a degree that it cannot right itself.

May be instead of "to knock down" I should use something else?