Question
What, pray tell, is the life cycle of "nimble will?"

How is it propagated?

Answer
Bob:

"Nimble Will" is a perennial grass which resembles crabgrass.  It begins to grow at Memorial Day and stops around Labor Day in the north.  It has stolons and seed which ensure propogation.

It is short and seeds low to the ground, making it hard to control by mowing.  Control via cultural methods are to favor the winter lawn with fertilization in fall and early spring when it is dormant.  Reseeding follows this step.

Mechanical means are physical removal and covering with plastic a larger area than the plant occupies (solarization.)

I do not like it.  Best wishes.