The instruments in Nanyin can be divided into the melodic (上四管) and the percussion (下四管) instruments. This other post touch a little on the melodic instruments of Nanyin. There are 4 instruments in the percussion or "xia si guan" section. A side note, the clapper (拍板), although a percussion instrument, does not fall within the percussion "xia si guan" section but within the melodic or "shang si guan" section. This is because the musician playing the clapper is also the singer, and even in cases of purely instrumental pieces, the clapper also falls under the category of melodic instruments.
In Nanyin music, rhythm is notated according to pai [拍] and liao [撩]. In Western classical music terms, we can think of the pai as the first beat in the bar and the liao as the rest of the beats. So a piece with 1 pai 3 liao can be thought of as corresponding to a 4/4 time.
In a piece of Nanyin music, the clapper always hits on the pai, or the main beat of the bar. The performance of the four percussion instruments: the xiangzhan [响盏], sibao [四宝], shuangyin [双音], and jiaoluo [叫锣] follows a strict set of rules.
The xiangzhan follows the rhythm of the pipa but never on the pai or the main beat. This means the xiangzhan will play exactly the same as the main melody, but omitting every time the note is on the main beat.
The sibao consists of 4 pieces of bamboo, the player holding 2 pieces in each hand. It also plays according to the rhythm of the pipa, including the pai or the main beat. When the pipa is playing nianzhi [捻指] (the closest English equivalent should be a tremolo), the sibao will do a tremolo as well, with the hands vibrating the pieces of bamboo. On the pai or main beats, the player will clap the pieces of bamboo together on separate hands, and on the rest of the notes, the player can play in a variety of ways, but always with the pieces of sibao from one hand hitting the other hand's.
The shuangyin is played on all the liao or all the beats of the bar except the first.
Finally, the jiaoluo which consists of a little gong and a temple block held in one hand, also has to follow a strict set of rules. The temple block is hit on every pai or main beat and the little gong is hit on the off beat of the liao, forming an interlocking rhythmical pattern with the shuangyin.