This can happen when they are drawing blood or inserting IV needles.
I used to draw a fair amount of blood back when I was nursing and so many people are easy to draw blood from and then there are those who drive you nutz. Their veins will role, or they dissapear when the weather is chilly.
Then there are the times when the needle will go into the wall of the vein and out the other side of the vein causing a leak of blood into the tissues like right now.
There are times when drawing blood that as you get the needles into the vein it will spasm causing it too become smaller in diameter which also causes the needle to sometimes gently slide out of the vein just a little. These are the ones that will have a slow leak and cause the hematoma which is another name for a big bruise.
Apply cold compresses, if needed to stop the leaking and if there is pain in the area then it helps to use a warm washcloth on the area. There is one nurse at my infusion center who is very good at inserting the needles for my monthly IVs. One month she got very close to a nerve that goes to the top of my thumb and that sucker hurt a lot for many months.
The nurses or techs don't do this on purpose, belive me. However, if you have a nurse/tech who always has problems and causes hematoma you might want to call in to the lab and talk to the manager. Sometimes a little inservice by management will give a person some knowledge that is needed to do a better job.
Also, if the manager is receiving a lot of complaints about the person they just may end up having to find a different way to make a living. Some people are just not good at drawing blood. The facts of life I guess. Good luck. IRish