The ornamental design for a side portion for an automobile, as shown and described.
FIG. 1 is a front perspective view of a side portion of an automobile showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a left side elevation view thereof; and,
FIG. 7 is a top plan view thereof.
The bottom view of the automobile forms no part of the claimed design. The portions of the photographs shown in light contrast form no part of the claimed design.