Nephi defended his people with his own arm (Jacob 1:10), as did Zeniff (Mosiah 9:16) and Benjamin (Words of Mormon 1:13). It is very probable that Limhi also fought alongside his people (Mosiah 20:8 implies that Limhi was among those fighting, even though it is not clearly stated). Alma now also goes up to battle.
The wording makes it appear that he does so primarily as the chief judge - or the political leader of the people of Zarahemla. It would appear that there is a long Nephite tradition of the armies being led by their leader, even though that leader might be aged, as Benjamin surely was at the time he wielded the sword of Laban in defense of his people.
It would not be unwarranted to assume that many of these leaders did actually participate in armed combat, as well as to assume that some were symbolic leaders in deference to age and position.
In any case, Alma is head of the army due to his position as chief judge. This leadership does not preclude the other officers of the army, and we may suppose that the majority of the military actions were carried out by these other captains and chief captains. This combat by chief leader will become an important facet of the main battle that will be the final focus of this chapter.