I know they changed the rules, but it just seems weird to salute when in civilian clothes.
I do it, and quite proudly.
Here is the actual text from the law:
SEC. 595. MILITARY SALUTE FOR THE FLAG DURING THE NATIONAL ANTHEM BY MEMBERS OF THE ARMED FORCES NOT IN UNIFORM AND BY VETERANS.
Section 301(b)(1) of title 36, United States Code, is amended by striking subparagraphs (A) through (C) and inserting the following new subparagraphs: ``(A) individuals in uniform should give the military salute at the first note of the anthem and maintain that position until the last note; ``(B) members of the Armed Forces and veterans who are present but not in uniform may render the military salute in the manner provided for individuals in uniform; and ``(C) all other persons present should face the flag and stand at attention with their right hand over the heart, and men not in uniform, if applicable, should remove their headdress with their right hand and hold it at the left shoulder, the hand being over the heart."
Note: Part (C) applies to those not in the military and non-veterans. The phrase "men not in uniform" refers to civil service uniforms like police, fire fighters, and letter carriers - non-veteran civil servants who might normally render a salute while in uniform.
Another lesser known custom is that you should face the flag which is in the position of honor, if there is more than one flag on display. So, you should face the huge flag at the north end of the stadium, unless there is a color guard on the field, displaying the colors.