McGuire gave the Rhinos hope with a diagonal run to the corner and he stretched out of a tackle from Jeffries to plant the ball over the line and then, three minutes before the break, Senior took Sinfield's pass to go through a gap and send Burrow over for a try.

BBC: Bradford 14-30 Leeds

Commendably, after the break, rather than sit back and plant men behind the ball, Hull went in search of the winner.

BBC: Chelsea 0-0 Hull

Ma-Kalambay bounded off his line but failed to make contact with the ball as Smith arrived on cue to plant a firm header into the net from 12 yards and hand Orient a shock lead.

BBC: Swansea 1-2 Leyton Orient

"In our studies, ball pressure made a big difference, " Dr. Plant said.

WSJ: Soccer 'Header' Impact Likened to Hard Punch

The size of the ball matters, too, with greater forces exerted by larger balls, said Dr. Plant.

WSJ: Soccer 'Header' Impact Likened to Hard Punch

And players should make sure the ball doesn't absorb water, since that makes it heavier, according to Dr. Plant.

WSJ: Soccer 'Header' Impact Likened to Hard Punch

The data showed the average forces of a soccer-ball header were similar to those exerted on the head by punches from amateur boxers, according to Daniel Plant, a researcher in Imperial's department of mechanical engineering, who presented the data Friday at a helmet-safety science conference at the university.

WSJ: Soccer 'Header' Impact Likened to Hard Punch