Will grass burns scar?

Depends injury/Rx : I assume you are asking about friction burns. If the wound is superficial ; does not have any dirt or other particlate matter embedded in it, is kept clean ; slightly moist and covered, and heals within 10-14 days, and the ensuing reddish area is protected by use of sunblock ; scar care creams then majority of these wounds heal with little or no sequelae. See a plastic surgeon, if concerned.