He was a half-brother of Sun Quan, the founding emperor of the state of Eastern Wu in the Three Kingdoms period.
Sun Lang was acting in capacity as a guardsman of the palace at the time and thus was under Lü Fan's authority.
However, early in the battle, he accidentally set fire to his own camp, destroying a large quantity of supplies in the process.
To compound the Wu forces' difficulty, a freak storm struck at Lü Fan's fleet, sending it crashing along the northern shore.
The general Xu Sheng arrived, driving back Cao Xiu's forces long enough for Lü Fan to regroup, and Cao Xiu's fleet was driven back.