The ornamental design for a footballlinementrainer, as shown and described.
FIG. 1 is a front perspective view of the football lineman trainer showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
The pair of tubular support frame members have bilaterally symmetric trapezoid profiles when viewed from the side. The broken lines are included for the purpose of illustrating portions of the football lineman trainer that form no part of the claimed design.