The joining of the two words 'Slide' and 'Tackle'.

Eg, a sliding tackle in football or as the Americans would call it, soccer.
Manager to player... "Will you Slackle that player next time instead of letting him run past you!"
by Troops May 22, 2011
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To slide tackle during a football match.

The joing of the 2 words SLIDE & TACKLE.
Will you slackle that player!!! He's taking the ball past you too bloody easy!
by Troops July 10, 2011
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