Stockport County were relegated to the Blue Square Bet North after losing 4-0 at Kidderminster, whose player Lee Vaughan was punched in a match marred by crowd trouble.
Play was suspended for 31 minutes at Aggborough when some County supporters raced on to the pitch after Anthony Malbon had given Harriers the lead.
Punches were thrown at players of both clubs, who were forced off the field.
When play resumed, Harriers won easily but missed out on automatic promotion.
However, it was the ugly crowd trouble which dominated the match - one week after disturbances involving
supporters following their matches against Wigan and Sunderland respectively.
Harriers defender Vaughan called the Stockport fan who assaulted him a "disgrace".
"I pulled one of the Stockport players away and a lad has come and hit me from behind," the 26-year-old told BBC Hereford and Worcester. "If I am being totally honest, those fans are an absolute disgrace.
"I am glad they are going down and I hope they go down again. My son was here today and he had to witness that.
"Coming on to the pitch and assaulting somebody oversteps the mark and when my kids and family are here, it is not nice."
Harriers manager Steve Burr blamed a "few mindless idiots" for the pitch invasion.
"The majority of Stockport County fans were there to support their team," he told BBC Sport. "It was just a few mindless idiots who wanted to spoil it for everyone else.
"They just came on and went for whoever they could get near. I saw someone strike out at Lee Vaughan and he's got a bit of a knock on the back of the head.
"You don't expect that on a football pitch. He's upset and disappointed."
Kidderminster went into the game knowing victory could have secured promotion to the Football League.
Mansfield's 1-0 win over Wrexham
means Harriers finished second in the table and will now meet Wrexham on Tuesday in the play-off semi-final first leg at the Racecourse Ground.
"County fans in the away section of the Railway Stand invaded the pitch and Vaughan was struck during a confrontation between players and fans."
By contrast, Stockport, whose 106-year stay in the Football League ended when they finished
bottom of League Two in 2011,
will now play in English football's sixth tier after finishing the season four points from safety.
After three wins in 15 games, around 1,200 Stockport fans arrived at Aggborough hoping their side would win and other results would go their way.
But Ian Bogie's team fell behind in the 51st minute when Malbon found the net.
That sparked an ugly pitch invasion and within a minute of the resumption, Harriers' top scorer Malbon cut inside to place home a left-foot shot for his second of the match and his 20th of the season.
Centre-half Cheyenne Dunkley headed Harriers' third after 57 minutes before substitute Martin Devaney scored his first goal for the club within 60 seconds of coming on, also with a header.
There was still time for Vaughan to miss a late penalty after Devaney had been fouled by Sam Sheridan, but by then Mansfield's promotion to the Football League had been confirmed.
A second relegation in three years continues a dismal fall from grace for Stockport, who competed in the former First Division [now the Championship] little more than a decade ago.
- 01 Lewis
- 02 L Vaughan
- 03 Demetriou
- 22 Dunkly
- 30 Gowling
- 04 Storer (Briggs - 68' )
- 08 Vincent
- 16 Jackman
- 10 Malbon (Devaney - 73' Booked )
- 11 Johnson
- 20 Gash (Rowe - 63' )
- 23 N Vaughan
- 18 Gittings
- 21 Briggs
- 26 Devaney
- 09 Rowe
- 01 Ormson
- 03 Newton
- 05 Vidal
- 06 Tunnicliffe
- 20 Fagbola
- 08 Kenyon Booked
- 14 Sheridan
- 22 Mainwaring Booked (Hackney - 53' )
- 31 Bullock (Marshall - 31' )
- 07 Whitehead
- 19 Cirak (Windsor - 60' )
- 02 Halls
- 18 Nolan
- 25 Hackney
- 27 Marshall
- 32 Windsor