Green’s Dictionary of Slang

a mild oath, lit. ‘God’s foot!’.

c.1590		Jeronimo (1605) D: Sfoot twas your fault my lord, you brought no word.
1601		Jonson Cynthia’s Revels V i: ’Sfoot, the carp has no tongue.
1607		Tourneur Revenger’s Tragedy (1967) I iii: ’Sfoot, the duke’s son.
1612		N. Field Woman is a Weathercock I ii: ’Sfoot! he shall have my bond to do him good.
c.1629		R. Brome City Wit III i: Sfoot, tis time to part you.
1631		J. Shirley School of Complement II i: ’Sfoot, he kisses her.
1639		Ford Lady’s Trial II i: ’Sfoot, Don, you talk too big.
1654		Witts Recreations Epigram No. 400: Z’foot, will you have of men more than their hearts?
1657		Marlowe Lascivious Queen IV ii: Oh! oh! s’life, s’foot, will you fight?
a.1661		‘The Devills Arse a Peake’ in Rump Poems and Songs (1662) ii 98: S’ foot! what if these Ars-worms with gifts of our gold.
1662		‘I.T.’ Thorny-Abbey I i: ’Sfoot, doe you think we gave him warning?
c.1815		J.K. Paulding Bucktails (1847) I ii: Why, she don’t care a fig about her neice [...] As for me – ’sfoot! I am become perfectly indifferent to her.