Wagner and captain Tim Southee had been seen in discussion prior to the wicket – whether the gesture and said discussion are linked is unknown.
Another possibility is that Wagner was directing it toward the departing batter van Tonder, but there had been no prior evidence to suggest any bad blood between the two.
Neil Wagner raises his middle finger towards someone as the Black Caps celebrate the wicket of South Africa's Raynard van Tonder. Photo / AFP
The Black Caps have staged something of a comeback on day three of the second test in Hamilton – taking the final six South African wickets for 33 runs after David Bedingham made 110 to put the pressure firmly back on the hosts.
Bowling the Proteas out for 235 has set New Zealand 267 to record a first-ever series victory over the South Africans – the Black Caps must first navigate a tricky evening session before having two full days of cricket to secure the win.
With the pitch beginning to favour spin conditions late in the match, New Zealand will look to their top order in Devon Conway, Tom Latham, Kane Williamson and Rachin Ravindra to lay a platform and make inroads into the total.