Adam Clarke on Psalms 18:26

With the froward - עקש ikkesh, the perverse man; he that is crooked in his tempers and ways.

Thou wilt show thyself froward - תתפתל tithpattal, thou wilt set thyself to twist, twine, and wrestle. If he contend, thou wilt contend with him. Thou wilt follow him through all his windings; thou wilt trace him through all his crooked ways; untwist him in all his cunning wiles; and defeat all his schemes of stubbornness, fraud, overreaching, and deceit.

My old Psalter has, With the wiked thow sal be wike. Here the term wicked is taken in its true original sense, crooked, or perverse. With the wiked, the perverse, thou wilt show thyself wike, i.e., perverse; from to draw back, to slide. As he draws back from thee, thou wilt draw back from him. It may, as before intimated, come from to seek for enchantments; leaving God, and going to devils; to act like a witch: but here it must mean as above. The plain import is, "If thou perversely oppose thy Maker, he will oppose thee: no work or project shall prosper that is not begun in his name, and conducted in his fear."