I claim the ornamental design for a baseball bat frame, as shown and described.
FIG. 1 is a perspective view of a baseball bat frame, showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof;
FIG. 5 is a rear elevational view thereof; and,
FIG. 6 is a left-side elevational view thereof, the right-side elevational view being a mirror image thereof.
The broken lines showing a team logo, mat cut-out, player number, and text on one of the bats in FIGS. 1 and 2 depict environmental matter and form no part of the claimed design.