לַמְנַצֵּ֣חַ אַל־תַּשְׁחֵת֮ לְדָוִ֪ד מִ֫כְתָּ֥ם בִּשְׁלֹ֥חַ שָׁא֑וּל וַֽיִּשְׁמְר֥וּ אֶת־הַ֝בַּ֗יִת לַהֲמִיתֽוֹ׃
For the Leader; Al-tashheth. [A Psalm] of David; Michtam; when Saul sent, and they watched the house to kill him.
Rashi on Psalms
al tashcheth He called the psalm by this name because he was close to dying and to being destroyed, and he begged for mercy in the matter.
Rashi on Psalms
and they guarded the house when Michal told them that he was ill (I Sam. 19:14) and she allowed him to flee at night.