©2020 Bradley Laird
Since the 4 notes are all stacked vertically it means they are played at the same time. In the real world we really think of most bluegrass as being played two beats to the measure. I will not go into a long discussion of this now, just know that time is all relative. You can either think of a measure as 4 beats and count "1-2-3-4" or you can think of it as 2 beats and count it "1-and-2-and". It still amounts to 4 "pulses of sound" and the offbeats would be the 2nd and 4th pulse.
This sort of thing is difficult to understand by reading about it so I highly recommend that you go watch this free video on understanding Bluegrass Rhythm Basics and also this free video on Basic Chop Chords if you haven't done so already.
Playing those bluegrass style mandolin chords is called chopping. It means to play one percussive chord on the offbeat, with a single quick downstroke of the pick, and then to slightly relax your fretting fingers to deaden the notes so they do not sustain. It may be easier to think of this action as squeezing the fingers to the frets just before you strike the strings with your pick and then releasing the pressure in between the pickstrokes. Your left hand fingers never lift off of the strings. The just allow the string to push up and off the frets to make the note nice and short.
I have seen a few folks attempt to get shortness in the chop by plopping their right hand down against the strings. It seems like a natural way to cut the chord off, but I must advise against it. Even though it may seem more intuitive. You want your right hand free to flow in an up and down motion and, if you use the heel of your right hand as a mute in between chords, you are introducing "in and out" motion and, even worse, the motion of the hand must stop. My advice: don't try to mute with your right hand.
When I used the word "percussive" in the previous description I mean "short" not violent or loud! I often see mandolin players who seem to think they must blast all four strings as hard as they can. There is no need for that! Just brush across the strings from 4th to 1st in a "quick stroke." Then damp the chord sound by releasing the pressure of the fretting fingers.
Here are some additional tips...
When you are ready go to Lesson 12.