Claims that a dead fox was fed to hounds in front of the public, on the first day after hunting with dogs was banned, are being investigated.
Hunting with dogs became illegal at midnight on Thursday
Sussex Police said it was also claimed a hunt monitor's vehicle was forced off a road at the Crawley and Horsham hunt.
In Kent, an anti-hunt campaigner was taken to hospital with minor injuries after an alleged assault.
Before meeting, hunts across the region had said they would hunt within the law. Neither force made arrests.
Police in Kent and Sussex said they attended meets only to ensure public safety and prevent disorder.
Kent Police said an assault on someone "who supports the Hunting Act" was alleged to have happened at Crundale, near Ashford, in east Kent.
Officers said that across the county, five pro-hunt events were held with hunt supporters and anti-hunt campaigners turning out in numbers.
"There were no other reported incidents at any other hunt gatherings," the force said.
Kent Police said before the ban came into force that events would be monitored, but arrests would not be made specifically for Hunting Act offences, in accordance with guidance issued by the Association of Chief Police Officers.
Four hunts took place across Sussex, attended by about 500 riders and 2,000 supporters, Sussex Police said.
"Hundreds of people attended hunts throughout the county, but despite the small number of incidents reported, all four hunts appear to have operated within the law," a spokesman said.
"Police will be investigating incidents including allegations by hunt monitors that their vehicle was forced off the road."
He said officers would be "discussing a number of issues" with the Crawley and Horsham hunt organisers including an allegation "that a dead fox was fed to hounds in front of members of the public".
The spokesman said: "This behaviour is unacceptable and unnecessarily provocative."
'Not looking for a fight'
On Friday, hunting with dogs became illegal with those ignoring the ban facing a risk of fines.
Nick Onslow, spokesman for the East Kent Hunt, which met in Crundale, told BBC Radio Kent: "There is anger at what the government has done to us, but we have been very clear to all of our supporters that we must try to turn the other cheek to any sort of intimidation.
"We are not looking for a fight.
The ban on hunting with dogs came into force on Friday
"The only fight we want is through the ballot box and through the courts."
He said the meet would hunt within the law and follow the three options now open to them which were to exercise the hounds, to use two hounds to flush out a fox and try to shoot it as it leaves cover, and to hunt a trail that had been laid beforehand.
Surrey Police said there was no violence at either of the two hunts in the county, and that the force had a uniformed presence at both.
A spokesman said there were a few verbal exchanges at the Old Surrey, Burstow and West Kent Hunt, but no arrests were made.