the first thing that comes to mind is SAQ training (speed, agility and quickness). There is actually quite a bit of information out there specific to Lacrosse, and this one looked good to me http://www.athletesacceleration.com/lacrossespeedtraining.html
I would recommend training core activation, deceleration, VMO activation (vastus medialis oblique fibers, but pretty much vastus medialis in general), the motions of all joints of the legs, proper absorption/dissipation/redirection of contact forces (bumping with other players), etc. If the player lacked power, I would include olympic lifts, box jumps/plyo (up mostly, down only from knee height or less), etc.
There are a number of other things that I might include depending on what I observe and assess in the client. I usually don’t give out advice without more information, so use this along with your judgement and own assessments of the client.