Pull crabgrass  when it is young.  A crabgrass seedling can look like this one day (about one inch tall),  and be as big as the plant below in just a couple of days.

Often, you will see the seed head sticking out before you see the plant.  If the plant you pull has a seed head, put it in the dumpster, not the compost pile.
 
History:  The government introduced crabgrass to the U.S. in 1849 for use as a forage plant.
 

Life Cycle:  Annual with fibrous root system, propagating by seeds and stems; rooting at nodes