[Konstantinos]

pawn Код:

new
    Killing_Spree[ MAX_PLAYERS ]
;

// OnPlayerConnect: 
Killing_Spree[ playerid ] = 0;

// OnPlayerDeath:
Killing_Spree[ playerid ] = 0;
if( killerid != INVALID_PLAYER_ID )
{
    Killing_Spree[ killerid ]++;
    switch( Killing_Spree[ killerid ] )
    {
        case 1: SetPlayerScore( killerid, GetPlayerScore( killerid ) + 1 );
        case 2 .. 60: SetPlayerScore( killerid, GetPlayerScore( killerid ) + 60 );
    }
}

Assuming you meant that on first killing spree, the player gets 1 score and from 2 to 60, the player gets 60 score.